Temperature-sensitive lethal mutant of era, a G protein in Escherichia coli

The era gene of Escherichia coli encodes a GTP-binding protein which has similarities to elongation factor Tu and the Saccharomyces cerevisiae RAS protein. To investigate its function, mutations affecting era were isolated. A mini-Tn10 insertion, which truncated 22 amino acids from the COOH end of Era, did not affect cell growth. By using this mini-Tn10 insert as a coselectable marker, a temperature-sensitive lethal era mutant was isolated by localized mutagenesis using P1 phage transduction. A single-base G to A change was found at position 23, causing a tyrosine residue to be substituted for the cysteine residue at position 8 (era-770), in addition to the COOH-terminal mini-Tn10 disruption. Both alterations were necessary for the temperature-sensitive phenotype. Purified Era-770 mutant protein exhibited reduced binding to GTP compared with that of the wild-type Era protein.