Visualization of replication-dependent DNA double-strand break repair in Escherichia coli

Chromosomal replication is a source of spontaneous DNA double-strand breaks (DSBs). In E. coli, DSBs are repaired by homologous recombination using an undamaged sister template. During repair, the RecA protein polymerizes on single-stranded DNA generated at the site of the DSB and catalyses the search for sequence homologies on the undamaged sister template. This study utilized fluorescence microscopy to investigate the spatial and temporal dynamics of the RecA protein at the site of a replication-dependent DSB generated at the lacZ locus of the E. coli chromosome. The DSB was generated by SbcCD-mediated cleavage of a hairpin DNA structure formed on the lagging strand template of the replication fork by a long palindromic sequence. The tandem insertion of a recA-mCherry gene with the endogenous recA gene at the natural chromosomal locus produced no detectable effect on cell viability in the presence of DSB formation. During repair, the fluorescently-labelled RecA protein formed a transient focus, which was inferred to be the RecA nucleoprotein filament at the site of the replication-dependent DSB. The duration of the RecA focus at the site of the DSB was modestly reduced in a ΔdinI mutant and modestly increased in a ΔuvrD or ΔrecX mutant. Most cells underwent a period of extended cohesion of the sister lacZ loci after disappearance of the RecA focus. Segregation of the sister lacZ loci was followed by cell division, with each daughter cell obtaining a copy of the fluorescently-labelled lacZ locus. The RecA focus at the site of the DSB was observed predominantly between the mid-cell and the ¼ position. In the absence of DSB formation, the lacZ locus exhibited dynamic movement between the mid-cell and the ¼ position until the onset of segregation. Formation of the DSB and initiation of repair occurred at the spatial localization for replication of the lacZ locus while the downstream repair events occurred very close to the mid-cell. Genomic analysis of RecA-DNA interactions by ChIP-seq was used to demonstrate that the RecA focus at the lacZ locus was generated by the repair of the palindrome-induced DSB and not the repair of one-ended DSBs emanating from stalled replication forks at the repressor-bound operator arrays. This study has shown that the repair of a replication-dependent DSB occurs exclusively during the period of cohesion of the sister loci and the repair is efficiently completed prior to segregation of the two sister loci

Codeine dysregulates ribosome biogenesis in Escherichia coli with DNA double-strand breaks to chart path to new classes of antibiotics

Aim: A bacterial genetics-guided approach was utilized for the discovery of new compounds affecting bacterial genome stability. Materials & methods: Fungal extracts and fractions were tested for genome instability-mediated antibacterial activity. Interaction assays and RT-qPCR were used to identify compounds that boost the activity of sub-minimum inhibitory concentration streptomycin and obtain insights on the molecular mechanisms of the primary hit compound, respectively. Results: Several extracts and fractions caused bacterial genome instability. Codeine, in synergy with streptomycin, regulates double-strand break (DSB) repair and causes bacterial ribosome dysfunction in the absence of DSBs, and dysregulation of ribosome biogenesis in a DSB-dependent manner. Conclusion: This study demonstrates a potential viable strategy that we are exploring for the discovery of new chemical entities with activities against Escherichia coli and other bacterial pathogens

Demographic and clinical characteristics of the HBsAg-negative participants.

Demographic and clinical characteristics of the HBsAg-negative participants.</p

Prevalence and demographic characteristics of occult hepatitis B virus infection in HBsAg-negative patients.

Prevalence and demographic characteristics of occult hepatitis B virus infection in HBsAg-negative patients.</p

Demographic characteristics of the haemodialysis patients.

Demographic characteristics of the haemodialysis patients.</p

HbcAb status of the HBsAg-negative patients.

Hepatitis B virus (HBV) infection is endemic in Ghana and chronic kidney disease patients on haemodialysis are a high-risk group for HBV infection. We determined the prevalence of overt and occult HBV infection among haemodialysis patients at the Korle Bu Teaching Hospital in Ghana. 104 consenting End Stage Renal Disease patients on long-term haemodialysis were recruited for the study and their socio-demographic, clinical and laboratory information were obtained using structured questionnaire. All the participants were tested for the hepatitis B surface antigen (HBsAg). The HBsAg-negative participants were re-tested for hepatitis B surface antibody (HBsAb), hepatitis B core antibody (HBcAb) and HBV DNA using chemiluminescence and Roche COBAS Ampli-Prep/TaqMan analyser and real-time polymerase chain reaction. Eight (7.7%) of the total participants were positive for HBsAg. Among the 96 HBsAg-negative participants, 12.5% (12) were HBcAb-positive, 7.3% (7) had detectable HBV DNA (mean = 98.7±53.5 IU/mL) and 40.6% (39) were positive for HBsAb. Five out of the 7 HBV DNA-positive participants were males and only one participant was negative for HBcAb. Seventy-three out of the 96 HBsAg-negative participants were vaccinated and 37 of these vaccinated individuals had significant HBsAb titres (mean = 423.21± 380.72 IU/mL). Our data demonstrated that the prevalence of overt and occult HBV infection among the haemodialysis (HD) patients was 7.7% and 7.3%, respectively, and only 50.7% of those who showed proof of vaccination were protected from HBV infection.</div

Predictors of occult hepatitis B virus infection.

Hepatitis B virus (HBV) infection is endemic in Ghana and chronic kidney disease patients on haemodialysis are a high-risk group for HBV infection. We determined the prevalence of overt and occult HBV infection among haemodialysis patients at the Korle Bu Teaching Hospital in Ghana. 104 consenting End Stage Renal Disease patients on long-term haemodialysis were recruited for the study and their socio-demographic, clinical and laboratory information were obtained using structured questionnaire. All the participants were tested for the hepatitis B surface antigen (HBsAg). The HBsAg-negative participants were re-tested for hepatitis B surface antibody (HBsAb), hepatitis B core antibody (HBcAb) and HBV DNA using chemiluminescence and Roche COBAS Ampli-Prep/TaqMan analyser and real-time polymerase chain reaction. Eight (7.7%) of the total participants were positive for HBsAg. Among the 96 HBsAg-negative participants, 12.5% (12) were HBcAb-positive, 7.3% (7) had detectable HBV DNA (mean = 98.7±53.5 IU/mL) and 40.6% (39) were positive for HBsAb. Five out of the 7 HBV DNA-positive participants were males and only one participant was negative for HBcAb. Seventy-three out of the 96 HBsAg-negative participants were vaccinated and 37 of these vaccinated individuals had significant HBsAb titres (mean = 423.21± 380.72 IU/mL). Our data demonstrated that the prevalence of overt and occult HBV infection among the haemodialysis (HD) patients was 7.7% and 7.3%, respectively, and only 50.7% of those who showed proof of vaccination were protected from HBV infection.</div

Characteristics of the HBsAg-negative OBI patients.

Characteristics of the HBsAg-negative OBI patients.</p

HBsAb immunity status of the HBsAg-negative patients.

HBsAb immunity status of the HBsAg-negative patients.</p