SUPPRESSION OF COLD-SENSITIVE SEC MUTATIONS IN ESCHERICHIA-COLI

Mutations in the secretory (sec) genes in Escherichia coli compromise protein translocation across the inner membrane and often confer condi tional-lethal phenotypes. We have found that overproduction af the cha peronins GroES and GroEL from a multicopy plasmid suppresses a wide ar ray of cold-sensitive sec mutations in E. coli. Suppression is accompa nied by a stimulation of precursor protein translocation. This multico py suppression does not bypass the Sec pathway because a deletion of s ecE is not suppressed under these conditions. Surprisingly, progressiv e deletion of the groE operon does not completely abolish the ability to suppress, indicating that the multicopy suppression of cold-sensiti ve sec mutations is not dependent on a functional groE operon. Indeed, overproduction of proteins unrelated to the process of protein export suppresses the secE501 cold-sensitive mutation, suggesting that prote in overproduction, in and of itself, can confer suppression. This mult icopy suppression is reminiscent of the previously characterized suppr essors of sec mutations which compromise protein synthesis and the obs ervation that low levels of protein synthesis inhibitors can suppress as well. In all cases, the mechanism of suppression is unrelated to th e process of protein export. We suggest that the multicopy plasmids al so suppress the sec mutations by compromising protein synthesis.