COLD SHOCK INDUCES A MAJOR RIBOSOMAL-ASSOCIATED PROTEIN THAT UNWINDS DOUBLE-STRANDED-RNA IN ESCHERICHIA-COLI

A 70-kDa protein was specifically induced in Escherichia coli when the culture temperature was shifted from 37 to 15 degrees C, The protein was identified to be the product of the deaD gene (reassigned csdA) en coding a DEAD-box protein, Furthermore, after the shift from 37 to 15 degrees C, CsdA was exclusively localized in the ribosomal fraction an d became a major ribosomal-associated protein in cells grown at 15 deg rees C. The csdA deletion significantly impaired cell growth and the s ynthesis of a number of proteins, specifically the derepression of hea t-shock proteins, at low temperature. Purified CsdA was found to unwin d double-stranded RNA in the absence of ATP, Therefore, the requiremen t: for CsdA in derepression of heat-shock protein synthesis is a cold shock-induced function possibly mediated by destabilization of seconda ry structures previously identified in the rpoH mRNA.