ABSTRACT
A divE mutant, which has a temperature-sensitive mutation in the tRNA1
Ser gene, exhibits differential loss of the synthesis of certain proteins, such as β-galactosidase and succinate dehydrogenase, at nonpermissive temperatures. In Escherichia coli, the UCA codon is recognized only by tRNA1
Ser. Several genes containing UCA codons are normally expressed after a temperature shift to 42°C in the divE mutant. Therefore, it is unlikely that the defect in protein synthesis at 42°C is simply caused by a defect in the decoding function of the mutant tRNA1
Ser. In this study, we sought to determine the cause of the defect in lacZ gene expression in thedivE mutant. It has also been shown that the defect inlacZ gene expression is accompanied by a decrease in the amount of lacZ mRNA. To examine whether inactivation of mRNA degradation pathways restores the defect in lacZ gene expression, we constructed divE mutants containingrne-1, rnb-500, and pnp-7 mutations in various combinations. We found that the defect was almost completely restored by introducing an rne-1 pnp-7 double mutation into the divE mutant. Northern hybridization analysis showed that the rne-1 mutation stabilized lacZ mRNA, whereas the pnp-7 mutation stabilized mutant tRNA1
Ser, at 44°C. We present a mechanism that may explain these results.