Magic spot metabolism in an Escherichia coli mutant temperature sensitive in elongation factor Ts

A temperature-sensitive mutant of Escherichia coli HAK88 which has been shown to have a lesion in elongation factor Ts (EFTs) was studied with repsect to its metabolism of guanosine 5'-diphosphate, 2'(3')-diphosphate (ppGpp) and the associated failure of ribosomal ribonucleic acid (rRNA) accumulation at the nonpermissive temperature. Results reported here show that (i) when EFTs is nonfunctional, a full complement of charged transfer RNA (tRNA) cannot prevent accumulation of ppGpp (magic spot) and the stringent failure of rRNA accumulation; (ii) chloramphenicol prevents magic spot (MS) formation and the stringent response not by increasing the percentage of charged tRNA, but possibly by somehow interfering directly with the synthesis of MS; and (iii) tetracycline can lead to MS disappearance without resumption of RNA synthesis. Thus, the absence of MS and the presence of a functional RNA polymerase and charged tRNA are not sufficient to support rRNA accumulation in vivo. An additional element in the regulatory system is suggested.