Characterization of cold-shock protein A of Antarctic Streptomyces sp. AA8321.

Polar organisms should have mechanisms to survive the extremely cold environment. Four genes encoding cold-shock proteins, which are small, cold-induced bacterial proteins, have been cloned from the Antarctic bacterium Streptomyces sp. AA8321. Since the specific functions of any polar bacterial or Streptomyces cold-shock proteins have not yet been determined, we examined the role of cold-shock protein A from Streptomyces sp. AA8321 (CspA(St)). Gel filtration chromatography showed that purified CspA(St) exists as a homodimer under physiological conditions, and gel shift assays showed that it binds to single-stranded, but not double-stranded, DNA. Overexpression of CspA(St) in Escherichia coli severely impaired the ability of the host cells to form colonies, and the cells developed an elongated morphology. Incorporation of a deoxynucleoside analogue, 5-bromo-2'-deoxyuridine, into newly synthesized DNA was also drastically diminished in CspA(St)-overexpressing cells. These results suggest that CspA(St) play a role in inhibition of DNA replication during cold-adaptation.