Resetting the Yeast Epigenome with Human Nucleosomes.

Humans and yeast are separated by a billion years of evolution, yet their conserved histones retain central roles in gene regulation. Here, we "reset" yeast to use core human nucleosomes in lieu of their own (a rare event taking 20 days), which initially only worked with variant H3.1. The cells adapt by acquiring suppressor mutations in cell-division genes or by acquiring certain aneuploid states. Converting five histone residues to their yeast counterparts restored robust growth. We reveal that humanized nucleosomes are positioned according to endogenous yeast DNA sequence and chromatin-remodeling network, as judged by a yeast-like nucleosome repeat length. However, human nucleosomes have higher DNA occupancy, globally reduce RNA content, and slow adaptation to new conditions by delaying chromatin remodeling. These humanized yeasts (including H3.3) pose fundamental new questions about how chromatin is linked to many cell processes and provide a platform to study histone variants via yeast epigenome reprogramming.

DASH/Dam1 complex mutants stabilize ploidy in histone-humanized yeast by weakening kinetochore-microtubule attachments.

Forcing budding yeast to chromatinize their DNA with human histones manifests an abrupt fitness cost. We previously proposed chromosomal aneuploidy and missense mutations as two potential modes of adaptation to histone humanization. Here, we show that aneuploidy in histone-humanized yeasts is specific to a subset of chromosomes that are defined by their centromeric evolutionary origins but that these aneuploidies are not adaptive. Instead, we find that a set of missense mutations in outer kinetochore proteins drives adaptation to human histones. Furthermore, we characterize the molecular mechanism underlying adaptation in two mutants of the outer kinetochore DASH/Dam1 complex, which reduce aneuploidy by suppression of chromosome instability. Molecular modeling and biochemical experiments show that these two mutants likely disrupt a conserved oligomerization interface thereby weakening microtubule attachments. We propose a model through which weakened microtubule attachments promote increased kinetochore-microtubule turnover and thus suppress chromosome instability. In sum, our data show how a set of point mutations evolved in histone-humanized yeasts to counterbalance human histone-induced chromosomal instability through weakening microtubule interactions, eventually promoting a return to euploidy.

Update of biomarkers to diagnose diabetic foot osteomyelitis: A meta-analysis and systematic review.

The aim of this study was to evaluate the diagnostic characteristics of biomarker for diabetic foot osteomyelitis (DFO). We searched PubMed, Scopus, Embase and Medline for studies who report serological markers and DFO before December 2022. Studies must include at least one of the following diagnostic parameters for biomarkers: area under the curve, sensitivities, specificities, positive predictive value, negative predictive value. Two authors evaluated quality using the Quality Assessment of Diagnostic Accuracy Studies tool. We included 19 papers. In this systematic review, there were 2854 subjects with 2134 (74.8%) of those patients being included in the meta-analysis. The most common biomarkers were erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and procalcitonin (PCT). A meta-analysis was then performed where data were evaluated with Forrest plots and receiver operating characteristic curves. The pooled sensitivity and specificity were 0.72 and 0.75 for PCT, 0.72 and 0.76 for CRP and 0.70 and 0.77 for ESR. Pooled area under the curves for ESR, CRP and PCT were 0.83, 0.77 and 0.71, respectfully. Average diagnostic odds ratios were 16.1 (range 3.6-55.4), 14.3 (range 2.7-48.7) and 6.7 (range 3.6-10.4) for ESR, CRP and PCT, respectfully. None of the biomarkers we evaluated could be rated as 'outstanding' to diagnose osteomyelitis. Based on the areas under the curve, ESR is an 'excellent' biomarker to detect osteomyelitis, and CRP and PCT are 'acceptable' biomarkers to diagnose osteomyelitis. Diagnostic odds ratios indicate that ESR, CRP and PCT are 'good' or 'very good' tools to identify osteomyelitis.

A versatile platform for locus-scale genome rewriting and verification.

Routine rewriting of loci associated with human traits and diseases would facilitate their functional analysis. However, existing DNA integration approaches are limited in terms of scalability and portability across genomic loci and cellular contexts. We describe Big-IN, a versatile platform for targeted integration of large DNAs into mammalian cells. CRISPR/Cas9-mediated targeting of a landing pad enables subsequent recombinase-mediated delivery of variant payloads and efficient positive/negative selection for correct clones in mammalian stem cells. We demonstrate integration of constructs up to 143 kb, and an approach for one-step scarless delivery. We developed a staged pipeline combining PCR genotyping and targeted capture sequencing for economical and comprehensive verification of engineered stem cells. Our approach should enable combinatorial interrogation of genomic functional elements and systematic locus-scale analysis of genome function.

Success of transmetatarsal amputation for limb salvage in patients with peripheral artery disease.

Limb salvage is a difficult path for patients to travel as there is no guarantee of the outcome, often the major factor is perfusion. For patients who underwent transmetatarsal amputation (TMA), success rate is crucial as the next option is most likely a major amputation. We performed a 10 years (2010-2020) retrospective review of patients that underwent a TMA and had an angiogram or computed tomography angiography (CTA) perioperatively at the Dallas VA Medical Center. Failure after TMA was defined as a patient requiring a proximal amputation within 1 year. There were 125 TMAs performed between 2010 and 2020 at the institution. Forty-four (35.2%) patients had an angiogram/CTA peri-operative and met the inclusion criteria. Seventeen subjects (38.6%) had a higher level of amputation. Of the 17 failures, 2 (11.8%) patients had no patent vessel runoff to the foot, 9 (52.9%) had one vessel, 4 (23.5%) had two vessels, and 2 (11.8%) had three vessels runoff. One vessel runoff to the foot yielded a high rate of poor outcomes (56.3%) defined as a higher level of amputation. Two or more vessels runoff to the foot had over 75% success of limb salvage with a TMA.

The Impact of Hospitalization for Diabetic Foot Infection on Health-Related Quality of Life: Utilizing PROMIS.

Diabetic foot infections (DFI) are an increasingly common cause of hospitalizations. Once hospitalized with DFI, many patients require some level of amputation, often undergoing multiple operations. With increasing importance on patient-centered metrics, self-reported health-related quality of life (HRQOL) tools have been developed. This prospective cohort study aimed assessed the impact of DFI on HRQOL. Two hundred twenty-four patients completed the 29-item Patient-Reported Outcome Measurement Information System (PROMIS) and 12-Item Short Form (SF-12) survey. Secondary outcomes using the Foot and Ankle Ability Measures survey were obtained and included in the analysis. The study group was comprised of hospitalized patients with DFIs (n = 120), and the control group was comprised of patients with diabetes who were evaluated for routine outpatient foot care (n = 104); diabetic foot screening, wound care, onychomycosis, and/or callosities. Using this cohort, a propensity score-matched sample of hospitalized patients with DFI (n = 35) and control group patients (n = 35) was created for comparative analysis. The 2-independent sample t test was used to test for group differences on each of the PROMIS subscale outcomes. Using PROMIS, we found that hospitalized patients with DFI reported significantly worse HRQOL in 6 of 7 subscales (physical function, anxiety, depression, fatigue, social role, pain intensity; p value range: .0001-.02) compared to outpatients with diabetes evaluated for routine foot care. There was no significant difference between the 2 groups on sleep disturbance (p = .22). Patients hospitalized for DFI report lower HRQOL compared to patients with diabetes receiving routine outpatient foot care.

Outcomes of Foot Infections Secondary to Puncture Injuries in Patients With and Without Diabetes.

It is difficult to compare foot infections in patients with diabetes to those without diabetes because foot infections are uncommon in people without diabetes. The aim of this study is to compare clinical outcomes in people with and without diabetes admitted to the hospital for an infected puncture wound. We evaluated 114 consecutive patients from June 2011 to March 2019 with foot infection resulting from a puncture injury; 83 had diabetes and 31 did not have diabetes. We evaluated peripheral arterial disease (PAD), sensory neuropathy, the need for surgery and amputation, length of hospitalization, and presence of osteomyelitis. Patients with diabetes were 31 times more likely to have neuropathy (91.6% versus 25.8%, p < .001, confidence interval [CI] 10.2 to 95.3), 8 times more likely to have PAD (34.9% versus 6.5%, p = .002, CI 1.7 to 35), and 7 times more likely to have kidney disease (19.3% versus 3.2%, p < .05, CI 0.9 to 56.5). They also took longer before presenting to the hospital (mean 20.1 ± 36.3 versus 18.8 ± 34.8 days, p = .09, CI 13 to 26.5); however, this result was not statistically significant. Patients with diabetes were 9 times more likely to have osteomyelitis (37.3% versus 6.5%, p = .001, CI 1.9 to 38.8). In addition, they were more likely to require surgery (95% versus 77%, p < .001, CI 1.6 to 21.4), required more surgeries (2.7 ± 1.3 versus 1.3 ± 0.8, p < .00001, CI 2.1 to 2.5), were 14 times more likely to have amputations (48.2% versus 6.5%, p < .0001, CI 3.0 to 60.2), and had 2 times longer hospital stays (16.2 ± 10.6 versus 7.5 ± 9 days, p = .0001, CI 11.9 to 15.9. Infected puncture wounds in patients with diabetes often fair much worse with more detrimental outcomes than those in patients without diabetes.

Erbium: Yttrium Aluminum Garnet Laser Accelerates Healing in Indolent Diabetic Foot Ulcers.

The objective of the study was to evaluate the effect of the erbium:yttrium aluminum garnet (YAG) laser on diabetic foot ulcers (DFUs) that had not responded to standard care. We retrospectively evaluated 22 nonhealing DFUs that received at least 4 weeks of standard wound care, demonstrated poor healing response, and subsequently were treated with an erbium:YAG laser. We measured the percent wound area reduction (PWAR) for the 4 weeks before initiating laser therapy and the PWAR for 4 weeks after the initiation of laser therapy. Erbium:YAG laser treatment consisted of 2 components: debridement and resurfacing. The laser settings were the same for all treatments. We used the paired t test to compare pretreatment with posttreatment wound area reduction. During the 4-week period before the initiation of laser therapy, the average PWAR was -33.6%. Four weeks after initiating treatment with the erbium:YAG laser, the average PWAR was 63.4% (p = .002) and 72.7% of wounds had ≥50% PWAR. By 12 weeks, 50% of wounds had healed. Erbium:YAG laser therapy accelerated DFU healing in a cohort of patients with ulcers that had been unresponsive to standard of care therapy.

Non-uraemic calciphylaxis successfully treated with pamidronate infusion.

Calciphylaxis is a rare and potentially fatal disease that affects the subcutaneous layer of the skin. It is a calcific vasculopathy induced by a systemic process that causes occlusion of small blood vessels. The mortality rate for individuals diagnosed with calciphylaxis is estimated between 52% and 81% with sepsis being the leading cause of death. Uraemic calciphylaxis and its known effective treatments are well documented in the literature. Unfortunately, there is no known effective treatment for non-uraemic calciphylaxis. Most of the current treatments for non-uraemic calciphylaxis are derived from uraemic calciphylaxis treatment protocols. We report a case of a 75-year-old female with calciphylaxis on the right lower extremity who was successfully treated with four pamidronate infusions in addition to local wound care. This case represents a non-uraemic calciphylaxis wound successfully treated with pamidronate infusions and standard wound care, and suggests that IV pamidronate can be an effective treatment option.

Elevated histone expression promotes life span extension.

Changes to the chromatin structure accompany aging, but the molecular mechanisms underlying aging and the accompanying changes to the chromatin are unclear. Here, we report a mechanism whereby altering chromatin structure regulates life span. We show that normal aging is accompanied by a profound loss of histone proteins from the genome. Indeed, yeast lacking the histone chaperone Asf1 or acetylation of histone H3 on lysine 56 are short lived, and this appears to be at least partly due to their having decreased histone levels. Conversely, increasing the histone supply by inactivation of the histone information regulator (Hir) complex or overexpression of histones dramatically extends life span via a pathway that is distinct from previously known pathways of life span extension. This study indicates that maintenance of the fundamental chromatin structure is critical for slowing down the aging process and reveals that increasing the histone supply extends life span.

Retrohoming of a Mobile Group II Intron in Human Cells Suggests How Eukaryotes Limit Group II Intron Proliferation.

Mobile bacterial group II introns are evolutionary ancestors of spliceosomal introns and retroelements in eukaryotes. They consist of an autocatalytic intron RNA (a "ribozyme") and an intron-encoded reverse transcriptase, which function together to promote intron integration into new DNA sites by a mechanism termed "retrohoming". Although mobile group II introns splice and retrohome efficiently in bacteria, all examined thus far function inefficiently in eukaryotes, where their ribozyme activity is limited by low Mg2+ concentrations, and intron-containing transcripts are subject to nonsense-mediated decay (NMD) and translational repression. Here, by using RNA polymerase II to express a humanized group II intron reverse transcriptase and T7 RNA polymerase to express intron transcripts resistant to NMD, we find that simply supplementing culture medium with Mg2+ induces the Lactococcus lactis Ll.LtrB intron to retrohome into plasmid and chromosomal sites, the latter at frequencies up to ~0.1%, in viable HEK-293 cells. Surprisingly, under these conditions, the Ll.LtrB intron reverse transcriptase is required for retrohoming but not for RNA splicing as in bacteria. By using a genetic assay for in vivo selections combined with deep sequencing, we identified intron RNA mutations that enhance retrohoming in human cells, but <4-fold and not without added Mg2+. Further, the selected mutations lie outside the ribozyme catalytic core, which appears not readily modified to function efficiently at low Mg2+ concentrations. Our results reveal differences between group II intron retrohoming in human cells and bacteria and suggest constraints on critical nucleotide residues of the ribozyme core that limit how much group II intron retrohoming in eukaryotes can be enhanced. These findings have implications for group II intron use for gene targeting in eukaryotes and suggest how differences in intracellular Mg2+ concentrations between bacteria and eukarya may have impacted the evolution of introns and gene expression mechanisms.

Epidemiology and Outcome of Microbial Keratitis: Private University Versus Urban Public Hospital Care.

PURPOSE: To review the epidemiology, risk factors, microbiologic spectrum, and treatment of microbial keratitis during a 5-year period at an urban public hospital in comparison with an adjacent private university practice. METHODS: Retrospective chart review in the 5-year interval, 2009 through 2014. Primary outcome measures included patient age at presentation, best-corrected visual acuity (BCVA), risk factors, culture and sensitivities, treatment, and complication occurrence. RESULTS: A total of 528 eyes with microbial keratitis were identified, 318 in the public cohort and 210 in the private cohort. Contact lens wear was the most common risk factor in the public cohort, whereas ocular surface disease was the most common risk factor in the private cohort. Gram-positive organisms represented 47.3%, gram-negative organisms 32.1%, fungal organisms 13.6%, and Acanthamoeba 6.4% of corneal isolates. Gentamicin resistance was 4.4% and tobramycin resistance was 2.9%. The inpatient treatment rate of the public cohort was 40% compared with 4% in the private cohort. In the public cohort, average BCVA at resolution was 20/82 (log of minimal angle of resolution [logMAR] 0.61). For the private cohort, average BCVA at resolution was 20/73 [logMAR, 0.56]. The perforation rate was 8% in the public cohort compared with 4% in the private cohort. Six percent of cases underwent urgent penetrating keratoplasty in the public cohort versus 2% in the private cohort. CONCLUSIONS: Microbial keratitis remains a clinical challenge in the urban public hospital setting. The risk profile of patients presenting in the public hospital setting may be different from patients presenting in a private care setting. Public hospital patients may present later in the course of their infection and thus have a higher rate of complications regardless of effective antimicrobial therapy.

Versatile genetic assembly system (VEGAS) to assemble pathways for expression in S. cerevisiae.

We have developed a method for assembling genetic pathways for expression in Saccharomyces cerevisiae. Our pathway assembly method, called VEGAS (Versatile genetic assembly system), exploits the native capacity of S. cerevisiae to perform homologous recombination and efficiently join sequences with terminal homology. In the VEGAS workflow, terminal homology between adjacent pathway genes and the assembly vector is encoded by 'VEGAS adapter' (VA) sequences, which are orthogonal in sequence with respect to the yeast genome. Prior to pathway assembly by VEGAS in S. cerevisiae, each gene is assigned an appropriate pair of VAs and assembled using a previously described technique called yeast Golden Gate (yGG). Here we describe the application of yGG specifically to building transcription units for VEGAS assembly as well as the VEGAS methodology. We demonstrate the assembly of four-, five- and six-gene pathways by VEGAS to generate S. cerevisiae cells synthesizing ß-carotene and violacein. Moreover, we demonstrate the capacity of yGG coupled to VEGAS for combinatorial assembly.

Genetic and biochemical assays reveal a key role for replication restart proteins in group II intron retrohoming.

Mobile group II introns retrohome by an RNP-based mechanism in which the intron RNA reverse splices into a DNA site and is reverse transcribed by the associated intron-encoded protein. The resulting intron cDNA is then integrated into the genome by cellular mechanisms that have remained unclear. Here, we used an Escherichia coli genetic screen and Taqman qPCR assay that mitigate indirect effects to identify host factors that function in retrohoming. We then analyzed mutants identified in these and previous genetic screens by using a new biochemical assay that combines group II intron RNPs with cellular extracts to reconstitute the complete retrohoming reaction in vitro. The genetic and biochemical analyses indicate a retrohoming pathway involving degradation of the intron RNA template by a host RNase H and second-strand DNA synthesis by the host replicative DNA polymerase. Our results reveal ATP-dependent steps in both cDNA and second-strand synthesis and a surprising role for replication restart proteins in initiating second-strand synthesis in the absence of DNA replication. We also find an unsuspected requirement for host factors in initiating reverse transcription and a new RNA degradation pathway that suppresses retrohoming. Key features of the retrohoming mechanism may be used by human LINEs and other non-LTR-retrotransposons, which are related evolutionarily to mobile group II introns. Our findings highlight a new role for replication restart proteins, which function not only to repair DNA damage caused by mobile element insertion, but have also been co-opted to become an integral part of the group II intron retrohoming mechanism.

Enhanced group II intron retrohoming in magnesium-deficient Escherichia coli via selection of mutations in the ribozyme core.

Mobile group II introns are bacterial retrotransposons thought to be evolutionary ancestors of spliceosomal introns and retroelements in eukaryotes. They consist of a catalytically active intron RNA ("ribozyme") and an intron-encoded reverse transcriptase, which function together to promote RNA splicing and intron mobility via reverse splicing of the intron RNA into new DNA sites ("retrohoming"). Although group II introns are active in bacteria, their natural hosts, they function inefficiently in eukaryotes, where lower free Mg(2+) concentrations decrease their ribozyme activity and constitute a natural barrier to group II intron proliferation within nuclear genomes. Here, we show that retrohoming of the Ll.LtrB group II intron is strongly inhibited in an Escherichia coli mutant lacking the Mg(2+) transporter MgtA, and we use this system to select mutations in catalytic core domain V (DV) that partially rescue retrohoming at low Mg(2+) concentrations. We thus identified mutations in the distal stem of DV that increase retrohoming efficiency in the MgtA mutant up to 22-fold. Biochemical assays of splicing and reverse splicing indicate that the mutations increase the fraction of intron RNA that folds into an active conformation at low Mg(2+) concentrations, and terbium-cleavage assays suggest that this increase is due to enhanced Mg(2+) binding to the distal stem of DV. Our findings indicate that DV is involved in a critical Mg(2+)-dependent RNA folding step in group II introns and demonstrate the feasibility of selecting intron variants that function more efficiently at low Mg(2+) concentrations, with implications for evolution and potential applications in gene targeting.

A comparison of sofosbuvir/velpatasvir and glecaprevir/pibrentasvir for the treatment of hepatitis C infection among people who inject drugs.

Background: To eliminate hepatitis C (HCV) infection as a public health concern by 2030, there is a need to develop comprehensive programs among key populations such as people who use drugs (PWUD). Two highly effective regimens are available for initial therapy: glecaprevir/pibrentasvir (G/P) given as 3 tablets/day for 8 weeks and sofosbuvir/velpatasvir (S/V) given as 1 tablet/day for 12 weeks. Data evaluating the safety and efficacy comparing one regimen over another in a population of PWUD is limited. Methods: Patients were identified through outreach events. Viremic patients were offered HCV treatment within a multidisciplinary program. This retrospective comparison analysis focuses on the first 120 sequential individuals who chose either treatment and in whom a definitive outcome of treatment was available between March 1, 2019 and February 29, 2024. The primary outcomes of the analysis were cure of HCV infection and its corelates, as well as safety of the individual regimens. Results: We successfully identified 120 within each of the G/P and S/V treatment groups. Of those on G/P, we note 28.3 % female, 20.9 % Indigenous, 70.8 % using fentanyl, and 51.3 % with unstable housing. Of those on S/V, we note 25.8 % female, 20.8 % Indigenous, and 75 % using fentanyl and 56.7 % with unstable housing. Overall, 118 and 115 patients completed therapy on G/P and S/V, respectively. A total of 118 and 115 completed therapy on G/P and S/V, with virologic relapse documented in 3 and 2 participants on G/P and S/V, respectively. The ITT/mITT cure rates for G/P and S/V were 95.0 %/97.4 % and 94.2 %/98.3 %, respectively. There were 5 drug overdose deaths among those who initiated treatment, one on G/P and 4 on S/V. Conclusion: We have evaluated two highly effective regimens in a group of inner-city PWUD, with comparable success rates well in excess of 90 %. Our data supports the offer of both options for the treatment of PWUD with HCV infection.

Lower extremity amputation rates in patients with chronic kidney disease: A database study comparing patients with and without diabetes mellitus.

Lower extremity amputation (LEA) is one of the most feared consequences of diabetes mellitus (DM). The purpose of this study was to evaluate the impact of DM on LEA rates in patients at various stages of chronic kidney disease (CKD). A commercially available de-identified database was searched for patients undergoing LEA and for CKD patients, from 2010 to 2023. Patients with DM and patients without DM who were followed for at least 5 years were included. LEA rates were then compared for patients at all 5 CKD stages in patients with and without diabetes. Rates of all LEA were found to be significantly higher at all CKD stages for patients with diabetes (overall, minor and major LEA). Compared to patients without DM who have CKD stage 5 (end stage renal disease), patients with DM and CKD stage 5 have a 30 fold increased likelihood of undergoing overall LEA [OR 30.2 (24.48-37.19), p < 0.001], 29 fold increased likelihood of undergoing minor LEA [28.9i (22.91-36.35), p < 0.001] and 40 times fold increased likelihood of undergoing major LEA [40.1 (26.59-60.42), p < 0.001]. For all stages of CKD, independent of diabetes status, minor LEA were performed with greater frequency than major LEA. In patients with DM, LEA rates significantly increased with CKD progression between stages 2-5 with a substantial jump between stages 4 and 5 [OR 2.6 (CI 2.49-2.74), p < 0.001]. However, CKD progression between stages 1 and 2 was not significantly associated with increased LEA rates (OR 1.1 (CI 0.92-1.21), p = 0.24) in patients with diabetes. Patients with comorbid diabetes have elevated risk for LEA at all stages of CKD compared to those without diabetes.

macroH2A1 drives nucleosome dephasing and genome instability in histone humanized yeast.

In addition to replicative histones, eukaryotic genomes encode a repertoire of non-replicative variant histones, providing additional layers of structural and epigenetic regulation. Here, we systematically replace individual replicative human histones with non-replicative human variant histones using a histone replacement system in yeast. We show that variants H2A.J, TsH2B, and H3.5 complement their respective replicative counterparts. However, macroH2A1 fails to complement, and its overexpression is toxic in yeast, negatively interacting with yeast's native histones and kinetochore genes. To isolate yeast with macroH2A1 chromatin, we uncouple the effects of its macro and histone fold domains, revealing that both domains suffice to override native nucleosome positioning. Furthermore, both uncoupled constructs of macroH2A1 exhibit lower nucleosome occupancy, decreased short-range chromatin interactions (<20 kb), disrupted centromeric clustering, and increased chromosome instability. Our observations demonstrate that lack of a canonical histone H2A dramatically alters chromatin organization in yeast, leading to genome instability and substantial fitness defects.

Does antibiotic treatment before bone biopsy affect the identification of bacterial pathogens from bone culture?

There is a common belief and practice that any exposure to oral or parenteral antibiotics prior to bone biopsy makes culture results unreliable. The aim of this article was to evaluate the effect of antibiotic exposure on bacterial yield in DFO microbiology specimens. The authors retrospectively evaluated 114 patients with DFO confirmed by histology. The primary outcome measurement was the proportion of bone biopsies with positive bacterial cultures. There was no statistically significant difference in culture yield in patients who received antibiotics (77.9%) and patients who did not (85.7%, P = .58). This study demonstrates that there were no differences in bacterial yield whether antibiotics were withheld or administered before bone cultures were obtained. The duration of antibiotic use prior to bone biopsy did not change the bacterial yield.

Human macroH2A1 drives nucleosome dephasing and genome instability in histone-humanized yeast.

In addition to replicative histones, eukaryotic genomes encode a repertoire of non-replicative variant histones providing additional layers of structural and epigenetic regulation. Here, we systematically replaced individual replicative human histones with non-replicative human variant histones using a histone replacement system in yeast. Variants H2A.J, TsH2B, and H3.5 complemented for their respective replicative counterparts. However, macroH2A1 failed to complement and its expression was toxic in yeast, negatively interacting with native yeast histones and kinetochore genes. To isolate yeast with "macroH2A1 chromatin" we decoupled the effects of its macro and histone fold domains, which revealed that both domains sufficed to override native yeast nucleosome positioning. Furthermore, both modified constructs of macroH2A1 exhibited lower nucleosome occupancy that correlated with decreased short-range chromatin interactions (<20 Kb), disrupted centromeric clustering, and increased chromosome instability. While supporting viability, macroH2A1 dramatically alters chromatin organization in yeast, leading to genome instability and massive fitness defects.