Acquirement of cold sensitivity by quadruple deletion of the cspA family and its suppression by PNPase S1 domain in Escherichia coli

Escherichia coli contains a large CspA family, CspA to CspI. Here, we demon strate that E. coli is highly protected against cold-shock stress, as these CspA homologues existed at approximately a total of two million molecules per cell at low temperature and growth defect was not observed until four c sp genes (cspA, cspB, cspE and cspG) were deleted. The quadruple-deletion s train acquired cold sensitivity and formed filamentous cells at 15 degreesC although chromosomes were normally segregated. The cold-sensitivity and fi lamentation phenotypes were suppressed by all members of the CspA family ex cept for CspD, which causes lethality upon overexpression. Interestingly, t he cold sensitivity of the mutant was also suppressed by the S1 domain of p olynucleotide phosphorylase (PNPase), which also folds into a beta -barrel structure similar to that of CspA. The present results show that cold-shock proteins and S1 domains share not only the tertiary structural similarity but also common functional properties, suggesting that these seemingly dist inct protein categories may have evolved from a common primordial RNA-bindi ng protein.