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Temperature-Sensitive Relaxed Phenotype in a Stringent Strain of Escherichia coli¹

^a Department of Genetics, Iowa State University, Ames, Iowa 50010

ABSTRACT

A temperature-sensitive elongation factor G (EF-G) mutation carried by a rel strain of Escherichia coli was transferred to a rel⁺ strain. The recombinant (AA-10) was found to be temperature-sensitive "relaxed" for ribonucleic acid (RNA) regulation. However, when a temperature-sensitive EF-G is present in a strain temperature-sensitive for valyl-transfer RNA (tRNA) synthetase, this new strain (AA-16) is no longer temperature-sensitive "relaxed" for RNA regulation. In strain AA-10, all tRNAs remain fully charged, and in AA-16 tRNA^val becomes completely discharged at the nonpermissive growth temperature. Also, synthesis of ppGpp is not observed in strain AA-10 at 42 C but is observed at 42 C in strain AA-16.

¹ Journal Paper no. J-7189 of Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa.