Abstract
BackgroundThe Staphylococcus aureus RecU protein is homologous to a Bacillus subtilis Holliday junction resolvase. Interestingly, RecU is encoded in the same operon as PBP2, a penicillin-binding protein required for cell wall synthesis and essential for the full expression of resistance in Methicillin Resistant S. aureus strains. In this work we have studied the role of RecU in the clinical pathogen S. aureus.ResultsDepletion of RecU in S. aureus results in the appearance of cells with compact nucleoids, septa formed over the DNA and anucleate cells. RecU-depleted cells also show increased septal recruitment of the DNA translocase SpoIIIE, presumably to resolve chromosome segregation defects. Additionally cells are more sensitive to DNA damaging agents such as mitomycin C or UV radiation. Expression of RecU from the ectopic chromosomal spa locus showed that co-expression of RecU and PBP2 was not necessary to ensure correct cell division, a process that requires tight coordination between chromosome segregation and septal cell wall synthesis.ConclusionsRecU is required for correct chromosome segregation and DNA damage repair in S. aureus. Co-expression of recU and pbp2 from the same operon is not required for normal cell division.
Highlights
The Staphylococcus aureus RecU protein is homologous to a Bacillus subtilis Holliday junction resolvase
We show that co-expression of recU and pbp2 from the same operon is not required for normal cell division
The fact that approximately half of the S. aureus cells grown in the absence of RecU had SpoIIIE-YFP foci, suggests that RecU has a major role in chromosome segregation, maybe through biasing recombination towards noncrossover products. (v) The presence of septa placed over the DNA, a phenotype that could be caused by segregation defects or, alternatively, by the lack of a cell division checkpoint required to prevent septum formation over the DNA
Summary
The Staphylococcus aureus RecU protein is homologous to a Bacillus subtilis Holliday junction resolvase. One example is the process of homologous recombination, required to re-establish stalled and collapsed replication forks and to repair double strand breaks (DSBs) [4,5]. The RecA protein associates with these overhanging strands, strand invasion occurs and a Holliday junction is formed and extended unidirectionally by branch migrating proteins such as RuvAB [6] Holliday junction resolvases, such as Bacillus subtilis RecU, have multiple roles during this process as they promote RecA-mediated strand invasion, associate with the branch migrating proteins and resolve the Holliday junction through DNA cleavage [7,8,9]. B. subtilis RecU biases homologous recombination towards non-crossover products, avoiding the formation of dimeric chromosomes that cannot be segregated to daughter cells in the absence of a compensating recombination reaction [11]
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