Complementation of cold shock proteins by translation initiation factor IF1 in vivo.

The cold shock response in both Escherichia coli and Bacillus subtilis is induced by an abrupt downshift in growth temperature and leads to a dramatic increase in the production of a homologous class of small, often highly acidic cold shock proteins. This protein family is the prototype of the cold shock domain (CSD) that is conserved from bacteria to humans. For B. subtilis it has been shown that at least one of the three resident cold shock proteins (CspB to D) is essential under optimal growth conditions as well as during cold shock. Analysis of the B. subtilis cspB cspC double deletion mutant revealed that removal of these csp genes results in pleiotropic alteration of protein synthesis, cell lysis during the entry of stationary growth phase, and the inability to differentiate into endospores. We show here that heterologous expression of the translation initiation factor IF1 from E. coli in a B. subtilis cspB cspC double deletion strain is able to cure both the growth and the sporulation defects observed for this mutant, suggesting that IF1 and cold shock proteins have at least in part overlapping cellular function(s). Two of the possible explanation models are discussed.