In order to determine the metabolic role of RNase D in Escherichia coli, we have attempted to isolate strains deficient in this enzyme. One strain containing a temperature-sensitive RNase D was found among a heavily mutagenized stock of strains temperature-sensitive for growth. Genetic mapping of the mutation responsible for the altered RNase D enabled us to define the rnd locus, at 39.5-40.0 min on the E. coli map, which apparently specifies the RNase D structural gene. Using a Tn 10 insertion near the rnd locus, we constructed isogenic strains containing RNase D and RNase II mutations, alone or in combination. Although the original mutant isolate displayed temperature-sensitive growth, no growth phenotype was associated with the rnd mutation in wild type background, possibly because a substantial amount of RNase D remained in cells grown at 45° C. However, elucidation of the map position of the rnd locus should prove useful for the isolation of other mutant strains with lower levels of RNase D.
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