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DNA clamp loader subunit DnaX gamma plays a role in the response to DNA damage
Author(s) -
Tashjian Tommy Fay,
Chien Peter
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.04041
Subject(s) - biology , genetics , dna damage , caulobacter crescentus , dna repair , microbiology and biotechnology , dna , gene , bacterial protein
The bacterial DNA damage response (DDR) is an important cellular system used to maintain a balance between maintenance of genomic integrity and mutagenesis that drives adaptation in the face of stress. An essential part of this response is the AAA+ protease ClpXP, which degrades several key DDR proteins. Our lab discovered a novel ClpXP substrate in Caulobacter crescentus , DnaX, a conserved component of the DNA replication clamp loader complex. DnaX has two forms: the essential full‐length DnaX tau and a shorter DnaX gamma. DnaX gamma is conserved in bacterial species, yet three distinct mechanism have been found to create it: ribosomal frameshift, transcriptional slippage, and partial ClpXP proteolysis in Caulobacter. Despite being discovered over 30 years ago, the function of DnaX gamma remains unclear. We find that a strain encoding nonproteolyzable version of DnaX (tau‐only), which does not contain any DnaX gamma has no observable growth or morphological defects, but is sensitive to certain types of DNA damage. While the DnaX tau‐only strain is not more sensitive than the wild type to ultra‐violet light, which primarily causes intra‐strand crosslinks, it is significantly more sensitive than wild type to mitomycin C and zeocin, which primarily cause inter‐ and intra‐strand crosslinks and double strand breaks, respectively. To better define the pathways that are affected in the absence of DnaX gamma, we performed transposon (Tn) sequencing analysis and found synthetically lethal and conditionally dispensable genetic interactions with the dnaX ‐ tau‐only allele. Even in normal growth conditions, we find several synthetic lethal interactions with this allele and DNA damage response genes, especially those involved in double‐strand break repair. We also find that the global transcriptional repressor of the DDR, LexA, is conditionally dispensable in our DnaX tau‐only strain. Together, this suggests a role for DnaX gamma in DNA damage prevention or repair under normal growth conditions and addresses the long‐standing question of why the shorter forms of DnaX are so broadly conserved in bacteria.