An Escherichia coli mutant with increased messenger ribonuclease activity.

A temperature-sensitive mutant strain of Escherichia coli exhibits a remarkable increase in RNase activity when grown at its nonpermissive temperature. During growth at the nonpermissive temperature, there is an increase in the extent of breakdown of pulse-labeled RNA and a decrease in the functional lifetime of the mRNA for the lac operon. T7 RNA, which is usually stable in E. coli, is also stable in this strain at the nonpermissive temperature. It is possible that the RNase measured is part of the normal mechanism of mRNA degradation in the cell. A mechanism for mRNA degradation that requires the combined action of endonuclease(s) and 3' to 5' exonuclease(s) is proposed.