Level of Methionyl‐tRNA Synthetase in Merodiploids of Escherichia coli K12

The specific activity of aminoacyl‐tRNA synthetases has been determined in strains of Escherichia coli K12 carrying the F32 episome. These strains were presumed to be diploid for the structural gene of methionyl‐tRNA synthetase. Of eighteen different aminoacyl‐tRNA synthetases tested, all but one showed similar levels of activity in both the merodiploids and the haploid strain of reference Hfr H. The only exception was methionyl‐tRNA synthetase, the level of which was four‐fold higher than that of the haploid strain, regardless of growth conditions. Parental strains of one of the merodiploids were studied. The female parent had the same level of methionyl‐tRNA synthetase as the hapoid HfrH strain, whilst the male parent Hfr AB 311, from which the F32 episome originated, had three times the level of the haploid HfrH strain. In both parental strains the level of valyl‐tRNA synthetase was the same as in the HfrH strain.