Intragenic suppression in the uvrD gene of Escherichia coli I. Temperature-sensitive uvrD mutations

A temperature-sensitive uvrD mutant, HD323 uvrD4, was isolated from the uvrD mutant HD4 uvrD3. The temperature sensitivity of the uvrD4 gene product was reversible. The suppressor mutation uvrD44 which rendered the uvrD3 mutant temperature-sensitive could be separated from the uvrD3 mutation by replacing the PstI fragment, which encodes the C-terminal half of the UvrD protein. The uvrD44 mutation was found to make host bacteria lethal at non-permissive temperatures only when cloned on a low copy vector pMF3. The nucleotide sequence of the uvrD3 and uvrD4 mutant genes was determined. The nucleotide change found in the uvrD3 at +1235, GAA to AAA, only alters the amino acid sequence from Glu at 387 to Lys. The uvrD44 has another nucleotide change at +1859, GAA to AAA (Glu at 595 to Lys), which is considered to be the suppressor mutation uvrD44.