[Blood eosinophils and clinical features of pneumoconiosis complicated with chronic obstructive pulmonary disease: A cross-sectional study].

Objective: To analyze the correlation between peripheral blood eosinophil (EOS) level and clinical characteristics of patients with pneumoconiosis complicated with chronic obstructive pulmonary disease (COPD) . Methods: From January 2007 to November 2020, newly diagnosed patients with pneumoconiosis complicated with COPD in Beijing Chaoyang Hospital, were retrospectively analyzed. These patients were stratified into EOS<100 cells/µl group and EOS≥100 cells/µl group, taking 100 cells/µl as the cut-off value. Demographic characteristics, clinical symptoms, lung function and laboratory indexes were compared between the two groups. Results: The median EOS count of patients with pneumoconiosis complicated with COPD was 100 (40, 180) cells/µl. 50.2% (160/319) had blood eosinophil counts ≥100 cells/µl, and 11.0% (35/319) had blood eosinophil counts ≥300 cells/µl. In comparison with EOS<100 cells/µl group, EOS≥100 cells/µl group were older (P=0.035), had higher body mass index (P=0.008), and had lower forced respiratory volume in the first second (P=0.017), had higher the ratio of residual volume to total lung volume (P=0.010), and had lower diffusing capacity of the lung for carbon monoxide (P=0.008). Arterial partial pressure of oxygen was significantly reduced in EOS≥100 cells/µl group (P=0.039). The peripheral blood EOS count was negatively correlated with forced vital capacity, forced breathing volume in the first second, carbon monoxide diffusion, peak expiratory flow, and maximum mid expiratory flow as a percentage of expected values (r(s)=-0.22, -0.18, -0.19, -0.19, -0.19, P=0.000, 0.001, 0.003, 0.008, 0.002), and positively correlated with the ratio of residual air volume to total lung volume (r(s)=0.17, P=0.002) . Conclusion: There was a correlation between blood EOS count and pulmonary function parameters, can proide reference for the diagnosis and treatment of chnoric obstuctive pulmmory disease in clinical practice.

[Effect of pirfenidone on paraquat-induced pulmonary fibrosis in rats].

Objective: To construct paraquat (PQ) poisoning rat model and to explore the effect of pirfenidone (PFD) on PQ-induced pulmonary fibrosis. Methods: In April 2017, male 6-8 week-old Wistar rats were selected, and PQ was administered intraperitoneally at one time. PFD was administered by gavage 2 hours after poisoning. The daily gavage doses were 100, 200 and 300 mg/kg, and the rats were divided into physiological saline group, PQ group, PQ+PFD 100 group, PQ+PFD 200 group, PQ+PFD 300 group, with 10 rats in each group at each observation time point. The pathological changes of lung tissue at different time points (the 1st, 3rd, 7th, 14th, 28th, 42nd and 56th days) after poisoning and the effect of PFD intervention with different dose on PQ-induced pulmonary fibrosis were observed. Pathological evaluation of lung tissue was performed by Ashcroft scale method. The PQ+PFD 200 group was selected to further explore the pathological changes of lung tissue, the contents of hydroxyproline and malondialdehyde in lung tissue were determined.And the tumor necrosis factor (TNF) -α, interleukin (IL) -6, transforming growth factor (TGF) -ß1, fibroblast growth factor (FGF) -B, platelet-derived growth factor (PDGF) -AB, insulin-like growth factor (IGF) -1 and PQ concentrations in serum and lung tissue were determined. Results: On the 1st to 7th day after PQ exposure, rats developed lung inflammation, which was aggravated on the 7th to 14th day, and pulmonary fibrosis appeared on the 14th to 56th day. Compared with PQ group, the Ashcroft scores of lung fibrosis in PQ+PFD 200 group and PQ+PDF 300 group decreased significantly in 7th and 28th day (P<0.05), while the Ashcroft score of lung fibrosis in PQ+PFD 100 group had no significant difference (P>0.05). After PQ exposure, the content of hydroxyproline in lung tissue increased gradually and reached the peak value on the 28th day. Compared with the PQ group, the contents of hydroxyproline in the PQ+PFD 200 group decreased at the 7th, 14th and 28th day, and the contents of malondialdehyde decreased at the 3rd and 7th day, the differences were statistically significant (P<0.05). The levels of TNF-α, IL-6 in rat serum and lung tissue reached the peak value on the 7th day after PQ exposure, and the levels of TGF-ß1, FGF-B and IGF-1 in rat serum and lung tissue reached the peak value on the 14th day after PQ exposure, and the level of PDGF-AB in rat serum and lung tissue reached the peak value on the 28th day after PQ exposure. Compared with PQ group, the level of serum IL-6 in PQ+PFD 200 group decreased significantly on the 7th day, and serum TGF-ß1, FGF-B, PDGF-AB and IGF-1 on the 14th and 28th day were decreased significantly (P<0.05). The levels of TNF-α, IL-6 in lung tissue of rats in PQ+PFD 200 group on the 7th day decreased significantly, and the levels of TGF-ß1, FGF-B and IGF-1 in lung tissue of rats on the 14th day were significantly decreased, and the level of PDGF-AB in lung tissue of rats on the 28th day were significantly decreased (P<0.05) . Conclusion: PFD partially alleviates the PQ-induced lung inflammation and fibrosis by inhibiting oxidative stress, reducing the levels of pro-inflammatory and pro-fibrotic cytokines in serum and lung tissue, but does not affect the concentrations of PQ in serum and lung tissue.

[Bibliometric and hot spot visualization analysis of pneumoconiosis and smoking].

Objective: To analyze the distribution and keywords of Chinese and English literature on pneumoconiosis and smoking, and to explore its characteristics and evolutionary laws. Methods: In November 2020, using PubMed, Web of Science, SinoMed, and CNKI as search databases, literature search was performed using Chinese and English search terms related to pneumoconiosis and smoking. The document management software Note Express 3.5.0 and the bibliometric analysis software VOS viewer 1.6.10 were used to analyze the publication year, number of publications, countries, research institutions and keywords. Results: In the English literature, there were 938 articles about pneumoconiosis and smoking related research, and the literature was first published in 1962. Among them, the United States published the largest number of articles (450 articles), and China published 29 articles, ranking fourth. There were a total of 601 research articles on pneumoconiosis and smoking in Chinese literature. The literature was first published in 1976. The institution that published the most articles was China Medical University (23 articles), followed by Lanzhou University (15 articles). Keyword co-occurrence analysis showed that domestic and foreign literatures were the main research hotspots on occupational exposure, carcinogenicity, risk factors, lung function, and DNA damage of pneumoconiosis and smoking. Conclusion: The research on pneumoconiosis and smoking focuses on carcinogenicity, risk factors, lung function, DNA damage mechanism, etc., providing research hotspots for the prevention and clinical treatment of related diseases.

[Chest high-resolution CT features analysis in predicting the progression of asbestosis].

Objective: To analyze the radiological characteristics of chest high-resolution computed tomography (HRCT) of patients with asbestosis, and to investigate the signs of predicting the disease progression of asbestosis. Methods: A prospective method was used to enroll 68 patients with asbestosis who were regularly followed up from 2013 to 2016. The radiological characteristics of patients with asbestosis were described by the International Classification of HRCT for Occupational and Environmental Respiratory Diseases (ICOERD) , and the differences between patients with and without progression were compared during the observation period. The Cox proportional hazards regression model was used to analyze the chest HRCT radiological signs predicting the progression of asbestosis. Results: The study included 68 patients with asbestosis aged (65.5±7.8) years old, of which 64.7% (44/68) were female, 29.4% (20/68) had a history of smoking. There was no significant difference in age, sex, smoking and asbestos exposure between patients with progressive asbestosis (20.6%, 14/68) and patients without progressive asbestosis (79.4%, 54/68) (P>0.05) . Chest HRCT of patients with asbestosis showed irregular and/or linear opacities, of which 5.9% (4/68) were accompanied by honeycombing. Irregular and/or linear opacities were mainly lower lung preponderant, often accompanied with ground glass opacity and mosaic perfusion. 98.5% (67/68) had pleural abnormalities, of which 39.7% (27/68) had diffuse pleural thickening with parenchymal bands and/or rounded atelectasis. The analysis of multivariable Cox proportional hazard regression showed that the risk of the progression of asbestosis was increased with higher irregular and/or linears opacities cores (HR=1.184, 95%CI: 1.012-1.384, P=0.034) and the appearance of honeycombing (HR=6.488, 95%CI: 1.447-29.097, P=0.015) . Conclusion: The irregular and/or linear opacities scores and honeycombing on chest HRCT are independent influencing factors for predicting the disease progression of asbestosis.

[Prevalence and risk factors of silicosis complicated with chronic obstructive pulmonary disease].

Objective: To explore the prevalence, clinical characteristics and risk factors of chronic obstructive pulmonary disease (COPD) in silicosis patients. Methods: In May 2021, a cross-sectional study was used to retrospectively include 329 silicosis patients first diagnosed in Beijing Chaoyang Hospital from January 1, 2007 to December 31, 2020. The demographic data, occupational history, chest imaging, pulmonary function and blood routine indicators of silicosis patients with COPD were analyzed, and the risk factors of silicosis with COPD were analyzed by multiple logistic regression. Results: There were 128 patients with silicosis complicated with COPD, and the overall prevalence rate was 38.9% (128/329) . Among them, 73.4% (94/128) were male and 33.6% (43/128) were heavy smokers; 33.6% (43/128) of patients were classified as gold 1, 37.5% (48/128) as gold 2, 25.0% (32/128) as gold 3, and 3.9% (5/128) as gold 4. Diagnostic age (OR=1.04, 95%CI=1.02~1.06, P<0.001) , cumulative smoking (OR=1.03, 95%CI=1.01~1.05, P=0.008) and silicosis stage III (OR=7.06, 95% CI=4.00-12.46, P<0.001) were risk factors for silicosis complicated with COPD. Conclusion: Diagnostic age, cumulative smoking volume and third stage of silicosis are the risk factors of silicosis patients with different degrees of COPD, which should be paid attention to in clinical treatment.

[A concise review of telomere and telomerase-related genetic markers in fibrotic lung diseases].

Fibrotic lung diseases are a heterogeneous group of diffuse parenchymal lung diseases caused by various factors. Pulmonary fibrosis is one of the common pathological changes of advanced fibrotic lung diseases. Idiopathic pulmonary fibrosis (IPF) is a chronic progressive fibrotic lung disorder with unknown etiology. IPF mainly affects the elderly that is considered as an aging related disease. Telomeres are specialized structures at the ends of chromosomes. Telomere shortening results in cellular senescence or apoptosis. Telomerase is a ribonucleoprotein complex that maintains telomere length and genome stability. The telomere shortening and mutations in telomere-related genes are associated with incidence and prognosis of pulmonary fibrosis. Here, a concise review of telomere and telomerase-related genomic markers in IPF and other fibrotic lung diseases is written.

[Real-life experience with pirfenidone in idiopathic pulmonary fibrosis].

Objective: To evaluate the efficacy and safety of pirfenidone (PFD) in idiopathic pulmonary fibrosis (IPF) in real-life world. Methods: 47 consecutive patients with IPF taking PFD for at least 12 months (PFD group) were included for analysis, with 47 patients with IPF who did not take PFD as controls. Data were collected from clinical charts to evaluate the lung function parameters and the adverse reactions of PFD. Results: In the PFD group, the percent predicted forced vital capacity (FVC%) and diffusing capacity of carbon monoxide (D(L)CO%) increased by (3.5±7.2)% and (1.1±6.1)% after 6 months of PFD treatment compared with the baseline, while the mean decline of FVC% and D(L)CO% was(2.3±6.7)% and (4.7±6.2)% in the controls (t=2.166, P=0.041; t=2.519, P=0.018). After 12 months of treatment, FVC% increased by (2.3±7.0)% and D(L)CO% decreased by(1.3±12.2)% compared with the baseline, while the mean decline of FVC% and D(L)CO% was (3.3±6.2)% and (5.3±9.8)% in the controls (t=2.292, P=0.030; t=1.047, P=0.303). In the PFD group, 17 patients regularly received pulmonary function test per 6 months. The mean decline in FVC% and D(L)CO% was(6.0±8.2)% and(7.0±13.3)% from 6 month before treatment to baseline when PFD was started, while the FVC% increased by (3.9±7.8)% and D(L)CO% increased by(1.3±6.6)% after 6 months of treatment compared with the baseline (Z=-2.897, P=0.004; Z=-2.151, P=0.031). The proportion of patients with more than 5% or 10% decline in FVC% decreased significantly after 6 months therapy (P=0.010 and 0.018, respectively). Adverse events were commonly seen in 30 patients while taking pirfenidone. The most common adverse events were gastrointestinal symptoms and skin reactions. Conclusions: In real-life world, PFD therapy for 12 months showed good effectiveness on pulmonary functions in patients with mild to severe IPF. Adverse events were common but mild.

Prediction of phosphorylation sites based on the integration of multiple classifiers.

Phosphorylation is an important part of post-translational modifications of proteins, and is essential for many biological activities. Phosphorylation and dephosphorylation can regulate signal transduction, gene expression, and cell cycle regulation in many cellular processes. Phosphorylation is extremely important for both basic research and drug discovery to rapidly and correctly identify the attributes of a new protein phosphorylation sites. Moreover, abnormal phosphorylation can be used as a key medical feature related to a disease in some cases. The using of computational methods could improve the accuracy of detection of phosphorylation sites, which can provide predictive guidance for the prevention of the occurrence and/or the best course of treatment for certain diseases. Furthermore, this approach can effectively reduce the costs of biological experiments. In this study, a flexible neural tree (FNT), particle swarm optimization, and support vector machine algorithms were used to classify data with secondary encoding according to the physical and chemical properties of amino acids for feature extraction. Comparison of the classification results obtained from the three classifiers showed that the classification of the FNT was the best. The three classifiers were then integrated in the form of a minority subordinate to the majority vote to obtain the results. The performance of the integrated model showed improvement in sensitivity (87.41%), specificity (87.60%), and accuracy (87.50%).

[Protective effect of Angelica sinensis polysaccharide against liver injury induced by D-galactose in aging mice and its mechanisms].

OBJECTIVE: To investigate the protective effect of Angelica sinensis polysaccharide (ASP) against liver injury induced by D-galactose in aging mice and its mechanisms. METHODS: Male C57BL/6J were randomly divided into three groups with 10 mice in each group. In the D-galactose model group, the mice were subcutaneously injected with D-galactose (120 mg/kg) qd×42; in the ASP+D-galactose group, from the 8th day of the establishment of D-galactose model, the mice were subcutaneously injected with ASP (120 mg/kg) qd×35. In the normal control group, the mice were subcutaneously injected with isotonic saline of the same volume at the same time point. On the 2nd day after the injection was finished, the ocular blood was collected to prepare serum and measure the content of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and total bilirubin (TBil). The liver tissue homogenate was prepared to measure the content of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), malondialdehyde (MDA), and advanced glycation end products (AGEs). A paraffin section of liver tissue was prepared; HE staining was performed to observe the pathomorphological changes of the liver, periodic acid-Schiff staining (PAS) was used to observe the changes in glycogen in the liver, and a transmission electron microscope was used to observe the hepatocyte ultrastructure. RESULTS: The D-galactose model group had increased content of ALT, AST, and TBil, reduced activities of SOD and GSH-Px, an increased content of MDA, and severe liver injuries; the hepatocytes showed degenerative changes, the amount of glycogen in the liver decreased, and the accumulation of AGEs increased. The ASP+D-galactose group had reduced content of ALT, AST, and TBil, increased activities of SOD and GSH-Px, and reduced content of MDA and AGEs; the amount of glycogen in the liver increased, and liver injury and hepatocyte injury were alleviated. CONCLUSION: ASP can antagonize the liver injury induced by D-galactose in aging mice, and its mechanism may be related to the inhibition of oxidative stress.

Assessing the interactions between the associations of common genetic variants on 2q35 and 16q12 with breast cancer risk.

UNLABELLED: Genome-wide association studies (GWAS) have identified 2q35 and 16q12 as breast cancer (BC) susceptibility loci. However, the association between the two polymorphisms and BC remains controversial and inconsistent. We therefore performed a more precise estimation of these relationships by meta-analysing the currently available evidence from the literature. The PubMed, Ovid, Medline and Web of Science databases were searched. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strengths of the associations. Thirty studies, including 106,312 cases and 140,939 controls, were identified. Overall, significantly elevated breast cancer risk was associated with the A allele of 2q35 rs13387042 when all studies were pooled into the meta-analysis (OR 1.11, 95%CI 1.07-1.15). Additionally, the T allele of 16q12 rs3803662 was associated with significantly increased breast cancer risk (OR 1.20, 95%CI 1.16-1.24). When stratifying for ethnicity, significantly increased risks were found among Caucasians, Asians and mixed ethnicities for both rs13387042 and rs3803662. For rs13387042, an association was observed for both oestrogen receptor-positive (ER+) (OR 1.14, 95%CI 1.11-1.17) and ER-negative (ER-) disease (OR 1.05, 95%CI 1.01-1.09) and for progesterone receptor-positive (PR+) (OR 1.16, 95%CI 1.12-1.19) and PR-negative (PR-) disease (OR 1.07, 95%CI 1.03-1.12). Similarly, a stronger association was observed for rs3803662 with ER+ tumors (OR 1.23, 95%CI 1.13-1.32) compared with ER- tumors (OR 1.08, 95%CI 0.97-1.20), and the same condition occurred for the polymorphism with PR+ tumors (OR 1.26, 95%CI 1.02-1.55) versus with PR- tumors (OR 1.15, 95%CI 0.90-1.46). When stratified by BRCA mutation status, a stronger association was observed with BRCA2 carriers (OR 1.23, 95%CI 1.05-1.44) than BRCA1 carriers (OR 1.09, 95%CI 1.04-1.15). In conclusion, this meta-analysis demonstrated that the A allele of 2q35 rs13387042 and the T allele of 16q12 rs3803662 are risk factors associated with increased breast cancer susceptibility. KEYWORDS: rs13387042, rs3803662, oestrogen receptor, progesterone receptor, breast cancer, meta-analysis.

Factors influencing epitaxial growth of three-dimensional Ge quantum dot crystals on pit-patterned Si substrate.

We investigated the molecular beam epitaxy growth of three-dimensional (3D) Ge quantum dot crystals (QDCs) on periodically pit-patterned Si substrates. A series of factors influencing the growth of QDCs were investigated in detail and the optimized growth conditions were found. The growth of the Si buffer layer and the first quantum dot (QD) layer play a key role in the growth of QDCs. The pit facet inclination angle decreased with increasing buffer layer thickness, and its optimized value was found to be around 21°, ensuring that all the QDs in the first layer nucleate within the pits. A large Ge deposition amount in the first QD layer favors strain build-up by QDs, size uniformity of QDs and hence periodicity of the strain distribution; a thin Si spacer layer favors strain correlation along the growth direction; both effects contribute to the vertical ordering of the QDCs. Results obtained by atomic force microscopy and cross-sectional transmission electron microscopy showed that 3D ordering was achieved in the Ge QDCs with the highest ever areal dot density of 1.2 × 10(10) cm(-2), and that the lateral and the vertical interdot spacing were ~10 and ~2.5 nm, respectively.

Gene expression analysis of ruptured and un-ruptured saccular intracranial aneurysm.

BACKGROUND: Although Saccular intracranial aneurysm (sIA) is the most common type abnormality of all intracranial aneurysms, the biological mechanisms of sIA are not fully understood. METHODS: We downloaded microarray datasets from Gene Expression Omnibus (GEO) database which includes 11 ruptured intracranial aneurysm samples and 8 unruptured intracranial aneurysm samples. Significant Analysis of Microarray (SAM) was employed to identify the differentially expressed genes (DEGs) between ruptured and unruptured intracranial aneurysms. RESULTS: We found 2129 genes differentially expressed in rupture sIA, of which 1062 genes up-regulated and 1057 genes down-regulated. Functional analysis demonstrated these genes were significantly associated with inflammatory response, wounding response and defense response. Protein-protein interaction (PPI) analysis revealed that these genes may play important roles in the pathogenesis of sIAs. Results suggested that four transcription factors (TFs) could cooperated with each other, together with several microRNAs play roles in the pathonegensis of ruptured sIAs. CONCLUSIONS: All of above results indicate the existence of DEGs between ruptured and unruptured sIAs, which regulating the pathogenesis of ruptured sIAs. TFs and microRNAs may also play key roles in ruptured sIAs. This research hints a new thought to the therapy of ruptured sIAs.

Evaluation and education of hydration and sodium status in a cool environment among Chinese athletes.

OBJECTIVE: The aim of the study was to find the significance of several factors with parameters of urine tests and blood tests. Finally, we aimed at evaluating the percentage of athletes from the study sample regarding their hydration level. SUBJECTS AND METHODS: The current study is the prospective type and was conducted on Chinese athletes between June 2021 to April 2022. The study was done in 2 parts for obtaining measurements in the summer season and the winter season and then they were correlated between them. Urine and blood samples were evaluated for determining the required parameters. The parameters of the physical environment like temperature, relative humidity, precipitation, etc. were obtained from the concerned weather station for each day. RESULTS: It was observed that 14.5%, 59% and 26.5% of the female participants were found to have hyper-hydrated, euhydrated and dehydrated, respectively. While 17.57%, 69.69% and 12.74% of the males were classified as hyper-hydrated, euhydrated and dehydrated, respectively. The participants with hyper-hydrated were found to have increased urine volume (p<0.001), reduced specific gravity (p<0.001) and reduced-sodium level (p<0.001). CONCLUSIONS: The study found that there is a significant difference in sodium levels between gender and seasons. The level of serum osmolality is also significantly different between the whole study populations concerning combined seasons. In this way, many other parameters are evaluated by correlation with seasons and gender. Hence, this study has brought forward various important findings and gives an overall evaluation of hydration status.

Influencing factors on the size uniformity of self-assembled SiGe quantum rings grown by molecular beam epitaxy.

The size uniformity of self-assembled SiGe quantum rings, which are formed by capping SiGe quantum dots with a thin Si layer, is found to be greatly influenced by the growth temperature and the areal density of SiGe quantum dots. Higher growth temperature benefits the size uniformity of quantum dots, but results in low Ge concentration as well as asymmetric Ge distribution in the dots, which induces the subsequently formed quantum rings to be asymmetric in shape or even broken somewhere in the ridge of rings. Low growth temperature degrades the size uniformity of quantum dots, and thus that of quantum rings. A high areal density results in the expansion and coalescence of neighboring quantum dots to form a chain, rather than quantum rings. Uniform quantum rings with a size dispersion of 4.6% and an areal density of 7.8×10(8) cm(-2) are obtained at the optimized growth temperature of 640°C.

Composition and strain measurements of Ge(Si)/Si(001) islands by HRTEM.

The distributions of the composition and the strain in the Ge(Si)/Si(001) coherent islands grown by molecular-beam epitaxy are investigated by digital analysis of high resolution transmission electron microscopy (HRTEM) micrographs. Local composition and strain are obtained from the measurement of the lattice displacement based on the Poisson's formula and Vegard's law. The analysis suggests that the islands have high Ge content at the island's central region. The island is partially relaxed by the substrate deformation and strain concentrated around the edge of islands. The alloying of the islands was found due to the Si surface diffusion.

Paper #18: Slow and gradual preoperative Halo Traction provides safe correction of severe scoliosis in patients with Osteogenesis Imperfecta.

This was a study of slow and gradual (at least 2 months) preoperative traction for osteogenesis imperfecta (OI). Results show that correction was significant with minimal complications after final fusion. Most significant correction in traction occurred within the 1st month but progressive correction was achieved beyond that.

Genetic organization and nucleotide sequence of the stability locus of IncFII plasmid NR1.

The stability (stb) locus of IncFII plasmid NR1 was mapped to a 1700 base-pair NaeI-TaqI restriction fragment. A series of unstable plasmids that contained insertion, deletion, and point mutations that inactivated the stability function was isolated. The unstable point mutants examined were all stabilized (complemented) in trans by a copy of the wild-type stb locus, suggesting that the mutations had inactivated diffusible gene products. The nucleotide sequence of the stb locus contained two tandem open reading frames, designated stbA and stbB, that encoded essential trans-acting protein products with predicted sizes of 36,000 Mr and 13,000 Mr, respectively. A third open reading frame, stbC, that could encode a peptide of 8000 Mr was contained within stbB in the complementary DNA strand. Plasmid-encoded proteins of 36,000 Mr and 13,000 Mr were identified in minicell experiments as the products of stbA and stbB, respectively. Unstable deletion mutants that retained the promoter proximal region of the stb locus upstream from stbA but had deleted both stbA and stbB were stabilized in trans by plasmids that could supply StbA and StbB. In contrast, deletion mutants that had lost the stbAB promoter region were not complemented in trans, indicating that this region contained an essential cis-acting site (or sites). Unlike some other loci that mediate stable plasmid inheritance, cloned copies of the wild-type stb locus of NR1 did not exert strong incompatibility (i.e. trans destabilization) against other stb+ derivatives of plasmid NR1 present in the same cell.

Complementation of mutants of the stability locus of IncFII plasmid NR1. Essential functions of the trans-acting stbA and stbB gene products.

A series of unstable mutants of the stability (stb) locus of IncFII plasmid NR1 was subjected to a complementation analysis. The mutant collection included plasmids with point, insertion and deletion mutations in stb. These mutations affected the tandem genes stbA and stbB, which encode stability proteins StbA and StbB, or the PAB transcription promoter, which is located upstream from stbA in a region that contains an essential cis-acting site. Deletion mutants that lacked the region containing promoter PAB could not be complemented (stabilized) by providing StbA and StbB in trans. Deletion mutants that lacked stbA and stbB but retained the PAB region were complemented in trans but required both StbA and StbB, indicating that both proteins were essential for stable inheritance. stbA- point mutants were complemented in trans by either wild-type or stbA+ stbB- clones of the stability region. However, mutants with insertions in stbA were complemented only by wild-type clones, which suggested the insertions were polar on expression of the downstream stbB gene. A plasmid with a stbB- point mutation was complemented in trans by wild-type but not by stbA- stbB+ clones. In addition, plasmid clones that expressed StbB in the absence of StbA caused destabilization of (were incompatible with) stb+ derivatives of NR1 in trans, whereas clones that expressed only wild-type StbA or both StbA plus StbB did not. Plasmid clones that contained only the essential cis-acting PAB region did not cause destabilization of stb+ plasmids in trans. These results suggest that an excess of StbB protein provided in trans may cause a depletion of the essential StbA protein. Therefore, these results may be consistent with the hypothesis that StbB is an autorepressor of the stbAB operon.