Radiation Desiccation Response Motif-Like Sequences Are Involved in Transcriptional Activation of the Deinococcal ssb Gene by Ionizing Radiation but Not by Desiccation

Abstract

ABSTRACT Single-stranded-DNA binding protein (SSB) levels during poststress recovery of Deinococcus radiodurans were significantly enhanced by 60 Co gamma rays or mitomycin C treatment but not by exposure to UV rays, hydrogen peroxide (H 2 O 2 ), or desiccation. Addition of rifampin prior to postirradiation recovery blocked such induction. In silico analysis of the ssb promoter region revealed a 17-bp palindromic radiation/desiccation response motif (RDRM1) at bp −114 to −98 and a somewhat similar sequence (RDRM2) at bp −213 to −197, upstream of the ssb open reading frame. Involvement of these cis elements in radiation-responsive ssb gene expression was assessed by constructing transcriptional fusions of edited versions of the ssb promoter region with a nonspecific acid phosphatase encoding reporter gene, phoN . Recombinant D. radiodurans strains carrying such constructs clearly revealed (i) transcriptional induction of the ssb promoter upon irradiation and mitomycin C treatment but not upon UV or H 2 O 2 treatment and (ii) involvement of both RDRM-like sequences in such activation of SSB expression, in an additive manner.