DNA damage response and cell cycle regulation in bacteria: a twist around the paradigm

Abstract

The co-protease activity in the RecA-ssDNA complex cleaves the autorepressor LexA, resulting in the derepression of a large number of genes under LexA control. This process is called the SOS response, and genes that are expressed in response to DNA damage are called SOS genes. The proteins encoded by the SOS genes are involved in both DNA repair and maintaining the functions of crucial cell division proteins (e.g., FtsZ) under check until the damaged DNA is presumably repaired. This mechanism of SOS response is the only known mechanism of DNA damage response and cell cycle regulation in bacteria. However, there are bacteria that do not obey this rule of DNA damage response and cell cycle regulation, yet they respond to DNA damage, repair it, and survive. That means such bacteria would have some alternate mechanism(s) of DNA damage response and cell cycle regulation beyond the canonical pathway of the SOS response. In this study, we present the perspectives that bacteria may have other mechanisms of DNA damage response and cell cycle regulation mediated by bacterial eukaryotic type Ser/Thr protein kinases as an alternate to the canonical SOS response and herewith elaborate on them with a well-studied example in the radioresistant bacterium Deinococcus radiodurans.

Keywords: DNA damage response; Deinococcus; Ser/Thr protein kinase; bacteria; cell cycle regulation; phosphorylation; radioresistance.

Figure 1

Schematic representation of eukaryotic-type γ radiation-responsive Ser/Thr quinoprotein kinase (RqkA) regulation of DNA damage response and cell cycle regulation in the radioresistant bacterium Deinococcus radiodurans. The γ radiation induces the synthesis of both RqkA and pyrroloquinoline quinone (PQQ). The PQQ activates the autokinase activity of RqkA, which is predicted to have a number of putative substrates in D. radiodurans that include DNA repair proteins such as RecA and PprA, and cell division proteins such as FtsZ. All three proteins undergo phosphorylation in vivo, and their phosphorylation showed a kinetic change during post-irradiation recovery. On one hand, the phosphorylation of RecA and PprA enhances their activity and is required for efficient function in the radioresistance of this bacterium. On the other hand, FtsZ phosphorylation makes it inferior, and it loses its dynamics in vivo.