Effects of apalutamide dose reduction on skin-related adverse events in patients with advanced prostate cancer: A multicenter retrospective study.

BACKGROUND: We aimed to evaluate the effects of apalutamide dose reduction on skin-related adverse events (AEs) and castration-resistant prostate cancer (CRPC)-free survival in patients with advanced prostate cancer (PC). METHODS: We retrospectively evaluated 35 patients with nonmetastatic CRPC and 72 patients with treatment-naïve metastatic castration-sensitive PC (mCSPC) who were treated with apalutamide. The primary outcome was the effect of apalutamide dose reduction on skin-related AEs. The secondary outcomes were the effect of apalutamide dose reduction on skin-related AEs in patients with small body size, postskin AE apalutamide discontinuation rate, and CRPC-free survival in patients with mCSPC treated with upfront apalutamide plus androgen deprivation therapy. RESULTS: Of the 107 patients, 65 (60.7%) and 42 (39.3%) were treated with full and reduced doses of apalutamide, respectively. The skin-related AE rate was not significantly different between the groups (55% vs. 43%, p = 0.761). In the group receiving reduced apalutamide dose, the incidence of skin-related AEs was significantly lower in patients with small body sizes (body weight <67 kg and body mass index <24 kg/m2 ) than in those with other body sizes. The postskin AE apalutamide discontinuation rate was significantly differed between patients receiving the full (50%) and reduced (16.7%) doses. In the 72 patients with mCSPC, CRPC-free survival was not significantly different between the full and reduced dose groups. CONCLUSION: Apalutamide dose reduction was not significantly associated with the incidence of skin-related AEs. However, dose reduction in patients with small body sizes may alleviate skin-related AEs without sacrificing oncological outcomes.

Development of a Cell-Based Assay Using a Split-Luciferase Reporter for Compound Screening.

Recently, the finding of recurrent mutations in the spliceosome components in cancer has indicated that the spliceosome is a potential target for cancer therapy. However, the number of small molecules known to affect the cellular spliceosome is currently limited probably because of the lack of a robust cell-based approach to identify small molecules that target the spliceosome. We have previously reported the development of a genetic reporter to detect the cellular levels of small nuclear ribonucleoproteins (snRNPs), which are subunits of the spliceosome, using a split luciferase. However, the original protocol was designed for small scale experiments and was not suitable for compound screening. Here, we found that the use of cell lysis buffer used in blue native polyacrylamide gel electrophoresis (BN-PAGE) dramatically improved the sensitivity and the robustness of the assay. Improved assay conditions were used to discover a small molecule that altered the reporter activity. Our method may be used with other cellular macromolecular complexes and may assist in the discovery of small bioactive molecules.

Impact of nephroureterectomy on postoperative renal function in upper tract urothelial carcinoma: A multicenter retrospective study.

OBJECTIVE: To assess the impact of radical nephroureterectomy on postoperative renal function in patients with upper tract urothelial carcinoma (UTUC). METHODS: We retrospectively evaluated 645 patients with UTUC treated with radical nephroureterectomy between January 2000 and May 2022. The primary outcome was the rate of postoperative estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2 . Secondary outcomes included the rate of eGFR decline, identification of factors related to eGFR decline, and the impact of comorbidities (diabetes or cardiovascular disease) on postoperative eGFR at 1 year. RESULTS: The median preoperative and postoperative eGFR levels were 55.6 and 43.3 mL/min/1.73 m2 , respectively. The rate of patients with preoperative and postoperative eGFR ≥60 mL/min/1.73 m2 was 40.9% and 9.0%, respectively. The median decline in eGFR after surgery was 25.1%. The presence of preoperative unilateral hydronephrosis and eGFR <60 mL/min/1.73 m2 was significantly associated with a low decline of postoperative eGFR and poor survival. The impact of the presence of comorbidities on postoperative eGFR at 1 year was significant (p < 0.001). CONCLUSION: Impaired renal function is prevalent in patients with UTUC. The rate of patients with postoperative eGFR ≥60 mL/min/1.73 m2 was 9.0%. The presence of preoperative renal impairment was significantly related to a low decline in postoperative eGFR and poor survival. The presence of comorbidities had a significant effect on eGFR decline 1 year after radical nephroureterectomy.

Effect of Liver Fibrosis on Oral and Gut Microbiota in the Japanese General Population Determined by Evaluating the FibroScan-Aspartate Aminotransferase Score.

The association between liver fibrosis and oral or gut microbiota has been studied before. However, epidemiological studies in the general population are limited owing to the difficulty of noninvasive liver-fibrosis assessment. FibroScan-asparate aminotransferase (FAST) scores can be used to accurately and non-invasively evaluate liver fibrosis. This study aimed to determine the association between liver fibrosis and oral or gut microbiota using the FAST score in the general population. After propensity score matching of 1059 participants based on sex, age, body mass index, homeostasis model assessment of insulin resistance, and triglyceride levels, 125 (non-liver-fibrosis group, 100; liver fibrosis group, 25) were included. The diversity of gut microbiota differed significantly between the two groups; however, no significant differences were noted in their oral microbiota. The liver fibrosis group showed an increase in the relative abundance of Fusobacteria strains and a decrease in the relative abundance of Faecalibacterium, with the presence of Fusicatenibacter in the gut microbiota. Feacalibacterium was not identified as an independent factor of liver fibrosis in adjusting the fatty liver index. In the general population, gut microbiota may be more involved in liver fibrosis than oral microbiota.

Association between reactive oxygen species production in neutrophils and liver fibrosis in the general population.

Fibrosis, induced by reactive oxygen species (ROS) production in neutrophils, has harmful effects on the liver and various other organs. However, little is known about the association between liver fibrosis and ROS levels in neutrophils in the general population. This large-scale epidemiological study aimed to determine the association between liver fibrosis and neutrophil-generated ROS levels according to age and sex in the general population. This cross-sectional study included 1,000 participants from a district health promotion project. Participants were grouped based on sex (male; female) and age (young, <65 years; old, ≥65 years). The four groups were as follows: male, young (n = 289); male, old (n = 100); female, young (n = 425); and female, old (n = 186). Liver fibrosis was assessed using the fibrosis 4 (FIB-4) index, aspartate aminotransferase-to-platelet ratio index (APRI), and non-alcoholic fatty liver disease (NAFLD) fibrosis score (NFS). Basal and stimulated ROS were considered in the analysis. Multiple linear analyses showed (1) significant positive correlations between all liver fibrosis scores and basal ROS in the young groups, and (2) significant negative correlations between NFS and stimulated ROS in females. Preventing liver fibrosis through neutrophil-related immune system enhancement may avert the development of lifestyle-related diseases and infections.

Periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis syndrome: Clinical characteristics and treatment outcomes - a single center study in Japan.

BACKGROUND: Periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis (PFAPA) syndrome is an autoinflammatory disease occurring in children. Although PFAPA is the most common periodic fever syndrome found in children, there are only a few studies defining the clinical characteristics and the efficacy of treatment strategies among Japanese children. This study aimed to clarify the demographic characteristics and clinical features of patients with PFAPA syndrome and to evaluate treatment efficacy. METHODS: We retrospectively reviewed the clinical features of children with PFAPA who visited Saitama Children's Medical Center between January and December 2019. We also evaluated treatment strategies and their efficacy; abortive treatment with corticosteroids, prophylaxis with cimetidine or colchicine, and surgical management with tonsillectomy. RESULTS: A total of 100 Japanese children (61% male) with PFAPA were included. Median age of onset was 3 years, median duration of fever episodes was 5 days, and median interval between episodes was 4 weeks. The symptoms (frequencies) were pharyngitis (89%), exudate on tonsils (71%), cervical adenitis (50%), and aphthous stomatitis (49%). Approximately 37% of patients took prednisolone for aborting fever attacks, showing a 100% response; 93% were treated with cimetidine, showing an 79.6% response, and 18% were treated with colchicine, showing a 66.7% response. Only one patient underwent tonsillectomy. CONCLUSIONS: Among Japanese children with PFAPA, 28% of them were ≥5 years with a male predominance. Pharyngitis is the most frequent symptom associated with fever. Cimetidine is suitable for initial therapy because of its safety and efficacy.

Recovering nutrients and rejecting trace organic compounds in human urine by a forward osmosis-membrane distillation (FO-MD) hybrid system.

Urine is a major source of reclaimed water and fertilizer. Urine treatment involves two key processes: the recovery of nutrients and the rejection of trace organic compounds (TOrCs). In this study, we investigated the rejection of TOrCs and the recovery of nutrients in human urine using a seawater-driven forward osmosis and membrane distillation (FO-MD) hybrid system. Three 24 h experiments were conducted at draw solution temperatures of 30, 40, and 50 °C. The average rejection rates of cations, anions, and dissolved organic carbon were more than 93.7% and 79.5% in the FO-MD system and FO side, respectively. Ten types of TOrCs were detected in the feed solution, whereas none were detected in the product water, indicating that the TOrCs were completely rejected. The precipitates, i.e., the recovered nutrients in the FO side, were extremely close to magnesium ammonium phosphate (struvite, MgNH4PO4·6H2O), according to their electron microscopic images, elemental composition, and X-ray diffraction spectra, and it was estimated that approximately 85% of the nutrients in the feed solution were recovered. The rejection and recovery efficiencies were unaffected by the draw solution temperature. These results indicate the potential for the sustainable use of FO-MD-based treatments for human urine.

Clinical impact of myositis-specific autoantibodies on long-term prognosis of juvenile idiopathic inflammatory myopathies: multicentre study.

OBJECTIVES: This study aimed to investigate the clinical characteristics, treatment and prognosis of juvenile idiopathic inflammatory myopathies (JIIM) in Japan for each myositis-specific autoantibody (MSA) profile. METHODS: A multicentre, retrospective study was conducted using data of patients with JIIM at nine paediatric rheumatology centres in Japan. Patients with MSA profiles, determined by immunoprecipitation using stored serum from the active stage, were included. RESULTS: MSA were detected in 85 of 96 cases eligible for the analyses. Over 90% of the patients in this study had one of the following three MSA types: anti-melanoma differentiation-associated protein 5 (MDA5) (n = 31), anti-transcriptional intermediary factor 1 alpha and/or gamma subunits (TIF1γ) (n = 25) and anti-nuclear matrix protein 2 (NXP2) (n = 25) antibodies. Gottron papules and periungual capillary abnormalities were the most common signs of every MSA group in the initial phase. The presence of interstitial lung disease (ILD) was the highest risk factor for patients with anti-MDA5 antibodies. Most patients were administered multiple drug therapies: glucocorticoids and MTX were administered to patients with anti-TIF1γ or anti-NXP2 antibodies. Half of the patients with anti-MDA5 antibodies received more than three medications including i.v. CYC, especially patients with ILD. Patients with anti-MDA5 antibodies were more likely to achieve drug-free remission (29 vs 21%) and less likely to relapse (26 vs 44%) than others. CONCLUSION: Anti-MDA5 antibodies are the most common MSA type in Japan, and patients with this antibody are characterized by ILD at onset, multiple medications including i.v. CYC, drug-free remission, and a lower frequency of relapse. New therapeutic strategies are required for other MSA types.

External validation of the EULAR/ACR idiopathic inflammatory myopathies classification criteria with a Japanese paediatric cohort.

OBJECTIVES: To assess the performance of the EULAR/ACR idiopathic inflammatory myopathies (IIMs) classification criteria to classify juvenile IIMs (JIIMs) in an Asian paediatric population. METHODS: Sixty-eight JIIM patients and 49 non-JIIM patients diagnosed at seven major paediatric rheumatology centres in Japan between 2008 and 2015 were enrolled. Retrospective data were collected, and each patient's data form was submitted. The expert group reviewed the forms and re-examined the diagnoses. The EULAR/ACR criteria were then applied and the probability of having JIIM was determined for each case. The sensitivity and specificity of the EULAR/ACR criteria were compared with those of other existing criteria. RESULTS: The sensitivity/specificity of the EULAR/ACR classification criteria were 92.1/100% with muscle biopsy data (n = 38); 86.7/100% without muscle biopsy data (n = 30) and 89.7/100% in our total cohort (n = 68). The sensitivity of Bohan and Peter's criteria and Tanimoto's criteria were 80.9 and 64.7% in our total cohort, respectively. Among 68 physician-diagnosed JIIM patients, seven cases (three JDM and four overlap myositis) were not classified as JIIM because the probability did not reach the cut-off point (55%). The three JDM patients all presented with only one of the three skin manifestations that are listed in the criteria: Gottron's sign. CONCLUSION: Our validation study with Japanese JIIM cases indicates that the EULAR/ACR classification criteria for IIM generally perform better than existing diagnostic criteria for myositis.

Efficacy, safety, and pharmacokinetics of oral valganciclovir in patients with congenital cytomegalovirus infection.

OBJECTIVES: Valganciclovir (VGCV) has been shown to improve sensorineural hearing loss (SNHL) and neurological outcomes in patients with neonatal symptomatic congenital cytomegalovirus (cCMV) infection. However, reports on the pharmacokinetics, efficacy and safety of oral VGCV are limited. The aim of this study is to evaluate the pharmacokinetics of VGCV for use in the treatment of cCMV. METHODS: This was a single-center, retrospective observational study conducted at Saitama Children's Medical Center in Japan between 2012 and 2017. CMV DNA copy number, maximum plasma VGCV concentration (Cmax), and adverse events (ADEs) during treatment were evaluated. RESULTS: A total of 26 patients with cCMV who received VGCV were included in this study. The median age at VGCV initiation was 9.5 months (range 0-46). Twenty-one patients (81%) had SNHL at baseline. Of these, five patients (19%) presented with improved SNHL, and none experienced worsened SNHL during treatment. The mean VGCV Cmax was 3.5 µg/mL (range 2-5.3), with no significant variation among individual values, and the values were maintained during treatment. Furthermore, there were no correlations between the Cmax values and age, sex, SNHL improvement or ADEs. Neutropenia (<1000/mm3) was observed in six patients (23%); however, no serious ADEs occurred. CONCLUSIONS: VGCV prevented the progression of SNHL without serious ADEs due to its stable pharmacokinetics. This study provides safety and tolerability of VGCV for the treatment of cCMV patients.

Infected simple renal cyst due to Streptococcus pneumoniae rapidly diagnosed by the melting temperature mapping method: a case report.

BACKGROUND: Spontaneous infection of preexisting solitary renal cysts has been documented in adults but is extremely rare in children. To date, no cases of simple renal cysts infected with Streptococcus pneumoniae have been described. Recently, reports have described the diagnosis of bacterial infection using the 16 S rRNA gene as well as the accompanying antimicrobial stewardship for microorganisms that are difficult to culture and for culture-negative cases after preceding antibacterial administration. CASE PRESENTATION: A four-year-old Japanese girl who had a pleuroperitoneal shunt inserted to drain a right pleural effusion due to occlusion of the hepatic portion of the inferior vena cava at three years old visited our hospital due to fever and respiratory discomfort. She was incidentally found to have a right simple renal cyst 10 months before admission. The patient was suspected to have pneumonitis or catheter-related blood stream infection on chest X-ray, which showed right-side pleural effusion. She was diagnosed with invasive pneumococcal infection, as Streptococcus pneumoniae was detected from blood culture on admission. Transient improvements in her symptoms and decreases in the white blood cell count and C-reactive protein level were observed after effective antibiotic administration, but her respiratory condition deteriorated. Enhanced CT showed right renal cyst enlargement and enhancement and thickening of the surrounding wall. Using the melting temperature (Tm) mapping method, S. pneumoniae was rapidly detected directly from pus 4.5 hours after drainage. The specimen culture was negative, but the extracted 16 S rDNA sequence revealed 100 % identity for S. pneumoniae from the same specimen the subsequent day. We successfully performed optimal treatment and reduced medical cost based on the positive Tm mapping method result. CONCLUSIONS: We report the first case of a S. pneumoniae-infected simple renal cyst. The drainage culture was negative, but the Tm mapping method rapidly detected S. pneumoniae directly from the drainage. The Tm mapping method may have great impacts on rapid diagnosis and effective antimicrobial stewardship.

Clinical practice guidance for juvenile dermatomyositis (JDM) 2018-Update.

Juvenile dermatomyositis is the most common type of juvenile idiopathic inflammatory myopathy mainly affecting the skin and proximal muscles. We have published the Japanese version of 'Clinical practice guidance for juvenile dermatomyositis (JDM) 2018 'consisting of a review of articles in the field and evidence-informed consensus-based experts' opinion on the treatment strategy in collaboration with The Pediatric Rheumatology Association of Japan and The Japan College of Rheumatology under the financial support by 'Research on rare and intractable diseases, Health and Labor Sciences Research Grants'. This article is a digest version of the Japanese guidance.

Pyogenic liver abscess due to hypervirulent Klebsiella pneumoniae in a 14-year-old boy.

A 14-year-old otherwise healthy boy presented with right-sided back pain following high fever. Abdominal computed tomography scan showed a large liver abscess. Klebsiella pneumoniae (KP) was rapidly identified from peripheral blood using the melting temperature mapping (Tm) method, which enables identification of pathogenic microorganisms within four hours after patient sample collection. He was diagnosed with pyogenic liver abscess (PLA) caused by KP on the day of admission. The KP was the hypervirulent (hv) clinical variant (string test positive, serotype K1, sequence type 23, rmpA and magA positive). After intravenous antibiotic therapy and drainage of the abscess, his condition resolved. The highlights of this case report are a healthy child with hypervirulent Klebsiella pneumoniae liver abscess in Japan and the new Tm mapping method for rapid and accurate identification of the pathogenic microorganism.

Influence of gastric endoscopic submucosal dissection on serum opsonic activity measured by chemiluminescence.

This study aimed to elucidate whether changes in serum opsonic activity measured by lucigenin-dependent chemiluminescence and luminol-dependent chemiluminescence are useful for estimating physical stress during the perioperative period of gastric endoscopic submucosal dissection. Serum opsonic activity in the peripheral blood of 87 patients was examined in the morning of the day of endoscopic submucosal dissection, the next day, and at 4 days after endoscopic submucosal dissection. Peak height and area under the curve for lucigenin-dependent chemiluminescence were 106.1 ± 22.7% and 102.0 ± 24.7% on the day of endoscopic submucosal dissection, which increased significantly to 113.6 ± 29.4% and 111.0 ± 29.1% on the next day (both p<0.01), and 112.4 ± 27.0% and 110.0 ± 28.1% at 4 days after endoscopic submucosal dissection (both p<0.01), respectively. In contrast, significant changes were not observed in peak height and area under the curve for luminol-dependent chemiluminescence during the perioperative period of endoscopic submucosal dissection. This difference suggests that serum opsonic activity during the perioperative period of gastric endoscopic submucosal dissection is associated with the production of substances with lower oxidizing potential. (The study of changes in neutrophil function and physical stress during the perioperative period of endoscopic operation: UMIN000034514).

Quantitative Analysis of Zigzag and Armchair Edges on Carbon Materials with and without Pentagons Using Infrared Spectroscopy.

Edge structures of carbon materials such as zigzag and armchair edges are known to affect their chemical and electronic properties. Although infrared spectroscopy (IR) has been known to be capable of identifying such edge structures, quantitative analysis using IR spectra has been conducted using only out-of-plane sp2C-H bending vibration, and the estimation of the percentage of edges is still challenging. In this work, a novel two-dimensional method to quantify edge structures of carbon materials with and without pentagons was developed by analyzing both out-of-plane sp2C-H bending and in-plane sp2C-H stretching vibration. Calibration factors of sp2C-H on each type of edge were obtained from experimental and simulated IR spectra of various reference compounds. Using the calibration factors, the edge structures of carbonized aromatic compounds with zigzag edges such as tetracene, armchair edges such as chrysene, and zigzag-like edges such as coronene were estimated quantitatively. From tetracene carbonized at 893 K, chrysene carbonized at 933 K, and coronene carbonized at 873 K, carbon materials with 20% of zigzag edges, 38% of armchair edges, and 67% of others edges were prepared, respectively. This method can be utilized as a quantitative analysis to determine edge structures of various carbon materials prepared below 933 K at the lowest.

Dimer-monomer equilibrium of human HSP27 is influenced by the in-cell macromolecular crowding environment and is controlled by fatty acids and heat.

Small heat shock protein 27 (HSP27) is an essential element of the proteostasis network in human cells. The HSP27 monomer coexists with the dimer, which can bind unfolded client proteins. Here, we evaluated the in-cell dimer-monomer equilibrium and its relevance to the binding of client proteins in a normal human vascular endothelial cell line. When cells were treated with a membrane-permeable crosslinker, the protein existed primarily as a free monomer (27 kDa) with a markedly smaller percentage of dimer (54 kDa), hetero-conjugates, and minor smear-like bands. When the protein was crosslinked in a cell-free lysate, two of the hetero-conjugates that were crosslinked in live cells were also detected, but the dimer and other complexes were absent. However, when cells were pretreated with fatty acid (FA) and/or heat (42.5 °C), dissociation of the dimer was selectively prevented and two types of covalently linked dimers were increased. These changes occurred most prominently in cells treated with docosahexaenoic acid (DHA) and heat, which appeared to intensify the heat resistance of the cell. Both the formation of covalently linked dimers and heat resistance were prevented by N-acetylcysteine. By contrast, nearly all of the free monomers in the lysate converted to disulfide bond-linked dimers by a simple, long incubation at 4 °C. These results strongly suggest that the monomer-dimer equilibrium of HSP27 was inversed between the in-cell and cell-free systems. Temperature- and amphiphile-regulated dimerization was restricted probably due to the low hydration of the in-cell crowding environment.

10-year follow-up of congenital cytomegalovirus infection complicated with severe neurological findings in infancy: a case report.

BACKGROUND: Congenital cytomegalovirus (cCMV) infection leads to sensorineural hearing loss (SNHL) and neurodevelopmental delays. However, the long-term outcomes of cCMV infection with severe neurological manifestations in infancy remain unclear. CASE PRESENTATION: The patient was a one-month-old girl visited owing to abnormalities in neonatal hearing screening. Central nervous system involvement including intracranial calcification and extensive white matter abnormalities was identified. Right SNHL (50 dB) was detected by auditory brain response (ABR) testing. The cause of her hearing loss was determined to be cCMV infection by polymerase chain reaction (PCR) using a dried blood spot. At 1.5 months of age, the patient was treated with intravenous ganciclovir (GCV) for 5 weeks followed by oral valganciclovir (VGCV) for an additional 6 weeks. Cytomegalovirus (CMV) loads in her urine continued to be detected until she was 10 years old. Fortunately, during this time, her right hearing loss did not deteriorate, and her left hearing remained normal. Furthermore, the extensive abnormal areas of white matter observed at 1 month of age mostly disappeared by the time the patient was 9 years old. Her neurodevelopmental score was normal, and motor milestones were not delayed as of 10 years of age. CONCLUSIONS: Here, we report the 10-year follow-up of a patient with cCMV who showed normal neurodevelopment, no progression of hearing loss, and ameliorating magnetic resonance imaging (MRI) findings, despite having various complications and severe neurological findings during infancy.

Clinical features of Stevens-Johnson syndrome and toxic epidermal necrolysis.

BACKGROUND: Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are rare, but these conditions are associated with high mortality. There have been few reports of SJS and TEN in children. The aim of this study was to evaluate the clinical features and outcomes of SJS and TEN in a group of Japanese children. METHODS: We retrospectively reviewed pediatric cases of SJS and TEN, from 2000 to 2015. RESULTS: We identified 12 pediatric cases of SJS and three of TEN. Six (all SJS) were caused by infection, and eight of the cases (SJS, n = 5; TEN, n = 3) were drug induced. Respiratory complications were the most common in terms of organ involvement, followed by hepatitis and gastrointestinal symptoms. Thirteen patients were treated with systemic corticosteroids, and two patients were treated with supportive therapy only. Concomitant with corticosteroid, four patients were given i.v. immunoglobulin. One patient with severe TEN was treated with systemic corticosteroids combined with plasmapheresis and cyclosporine. None of the present patients died. One patient with TEN had severe sequelae, with bronchiolitis obliterans and ocular involvement. CONCLUSIONS: SJS/TEN are rare, but are associated with severe complications. General pediatricians need to have up-to-date information regarding these conditions. The present study provides insights into the confirmation of the risk of SJS/TEN as well as the treatment of these diseases.

The N-Terminal Domain of Ribosomal Protein L9 Folds via a Diffuse and Delocalized Transition State.

The N-terminal domain of L9 (NTL9) is a 56-residue mixed α-ß protein that lacks disulfides, does not bind cofactors, and folds reversibly. NTL9 has been widely used as a model system for experimental and computational studies of protein folding and for investigations of the unfolded state. The role of side-chain interactions in the folding of NTL9 is probed by mutational analysis. ϕ-values, which represent the ratio of the change in the log of the folding rate upon mutation to the change in the log of the equilibrium constant for folding, are reported for 25 point mutations and 15 double mutants. All ϕ-values are small, with an average over all sites probed of only 0.19 and a largest value of 0.4. The effect of modulating unfolded-state interactions is studied by measuring ϕ-values in second- site mutants and under solvent conditions that perturb unfolded-state energetics in a defined way. Neither of these alterations significantly affects the distribution of ϕ-values. The results, combined with those of earlier studies that probe the role of hydrogen-bond formation in folding and the burial of surface area, reveal that the transition state for folding contains extensive backbone structure and buries a significant fraction of hydrophobic surface area, but lacks well developed side-chain-side-chain interactions. The folding transition state for NTL9 does not contain a specific "nucleus" consisting of a few key residues; rather, it involves extensive backbone hydrogen bonding and partially formed structure delocalized over almost the entire domain. The potential generality of these observations is discussed.