Kimble, M. | bioRxiv Science

bioRxiv2022

Characterization of the cluster MabR prophages of Mycobacterium abscessus and Mycobacterium chelonae

Mycobacterium abscessus is an emerging pathogen of concern in cystic fibrosis and immunocompromised patients and is considered one of the most drug-resistant mycobacteria. The majority of clinical M. abscessus isolates carry one or more prophages that are hypothesized to contribute to virulence and bacterial fitness. The prophage McProf was identified in the genome of the Bergey strain of M. chelonae, and is distinct from previously described prophages of M. abscessus. The McProf genome increases intrinsic antibiotic resistance of M. chelonae and drives expression of the intrinsic antibiotic resistance gene, whiB7, when superinfected by a second phage. The prevalence of McProf-like genomes was determined in sequenced mycobacterial genomes. Related prophage genomes were identified in the genomes of 25 clinical isolates of M. abscessus and assigned to the novel cluster, MabR. The MabR genomes share less than 10% gene content with previously described prophages; however, share features typical of prophages, including polymorphic toxin immunity (PT-Imm) systems.

genomics↗

bioRxiv2018

Sae2 antagonizes Rad9 accumulation at DNA double-strand breaks to attenuate checkpoint signaling and facilitate end resection

The Mre11-Rad50-Xrs2NBS1 complex plays important roles in the DNA damage response by activating the Tel1ATM kinase and catalyzing 5-3 resection at DNA double-strand breaks (DSBs). To initiate resection, Mre11 endonuclease nicks the 5 strands at DSB ends in a reaction stimulated by Sae2CtIP. Accordingly, Mre11-nuclease deficient (mre11-nd) and sae2{Delta} mutants are expected to exhibit similar phenotypes; however, we found several notable differences. First, sae2{Delta} cells exhibit greater sensitivity to genotoxins than mre11-nd cells. Second, sae2{Delta} is synthetic lethal with sgs1{Delta}, whereas the mre11-nd sgs1{Delta} mutant is viable. Third, Sae2 attenuates the Tel1-Rad53CHK2 checkpoint and antagonizes Rad953BP1 accumulation at DSBs independent of Mre11 nuclease. We show that Sae2 competes with other Tel1 substrates, thus reducing Rad9 binding to chromatin and to Rad53. We suggest that persistent Sae2 binding at DSBs in the mre11-nd mutant counteracts the inhibitory effects of Rad9 and Rad53 on Exo1 and Dna2-Sgs1 mediated resection, accounting for the different phenotypes conferred by mre11-nd and sae2{Delta} mutations. Collectively, these data show a resection initiation independent role for Sae2 at DSBs by modulating the DNA damage checkpoint.

genetics↗