A reliable response to DNA damage is essential for living organisms to survive 1. The consequences of DNA damage range from reduced fitness to various diseases such as cancer 2,3.
Bacillus subtilis (B. subtilis) reacts to DNA damage by invoking the SOS response, which is controlled and directed by the protein RecA and the transcriptional repressor LexA4,5.
A gen-operon that has been understudied concerning SOS response contains yhaO-sbcE-yhaM. YhaM (yhaM) has been characterized as a member of a family of 3'-exoribonucleases bearing hydrolytic ribonuclease activity. It is characterized by its unique composition and arrangement of domains. The protein consists of an N-terminal oligonucleotide domain (OB) and a C-terminal metal-dependent phosphohydrolase domain (HD). The involvement of YhaM could be demonstrated for different pathways of RNA degradation 6,7. The specific function of YhaM is not clear 8.
Here, we introduce YhaM as a new member of the bacterial SOS response machinery.
Structural characterization revealed the formation of a hexamer ring where the individual monomers are assembled in a head-to-tail conformation. The hexamer interface is formed by the phosphohydrolase domain (HD) and the oligonucleotide binding domains decorate the opening of the resulting pore. Our biochemical data, in combination with in vivo experiments, led to a hypothesis where the OB domain acts as a scanner for hydrolysis identifying chromosomal locations activity. We observed that the loss of yhaM leads to a Mitomycin C (MMC) sensitive phenotype. Microscopy analyses showed that YhaM accumulates together with RecA during DNA damage, especially when double-strand breaks are formed by MMC, and has a role in the repair mechanism. This suggests that YhaM has its site of action on DNA, which is further corroborated by the finding that the overproduction of YhaM results in a replication block and highly condensed DNA.
Therefore, we introduce YhaM as a new member of bacterial SOS response machinery, based on its structural and catalytic properties.
Friedberg, et al. American Society for Microbiology Press (2005)Funchain, et al. Genetics (2000)Tubbs, et al. Cell (2017)Goranov, et al. Journal of bacteriology (2006)Au, et al. Journal of bacteriology (2005)Redko, et al. Journal of bacteriology (2010)Oussenko, et al. Journal of bacteriology (2002)Bechhofer, et al. Critical reviews in biochemistry and molecular biology (2019)