CspI, the Ninth Member of the CspA Family of Escherichia coli , Is Induced upon Cold Shock

Abstract

ABSTRACT Escherichia coli contains the CspA family, consisting of nine proteins (CspA to CspI), in which CspA, CspB, and CspG have been shown to be cold shock inducible and CspD has been shown to be stationary-phase inducible. The cspI gene is located at 35.2 min on the E. coli chromosome map, and CspI shows 70, 70, and 79% identity to CspA, CspB, and CspG, respectively. Analyses of cspI-lacZ fusion constructs and the cspI mRNA revealed that cspI is cold shock inducible. The 5′-untranslated region of the cspI mRNA consists of 145 bases and causes a negative effect on cspI expression at 37°C. The cspI mRNA was very unstable at 37°C but was stabilized upon cold shock. Analyses of the CspI protein on two-dimensional gel electrophoresis revealed that CspI production is maximal at or below 15°C. Taking these results together, E. coli possesses a total of four cold shock-inducible proteins in the CspA family. Interestingly, the optimal temperature ranges for their induction are different: CspA induction occurs over the broadest temperature range (30 to 10°C), CspI induction occurs over the narrowest and lowest temperature range (15 to 10°C), and CspB and CspG occurs at temperatures between the above extremes (20 to 10°C).