Reduced Lactose Operon Expression in an Escherichia Coli Mutant Lacking Leucyl, Phenylalanyl-tRNA: Protein Transferase
Freedman, Leonard P.
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A mutant of Escherichia coli has been isolated which lacks leucyl, phenylalanyl-tRNA:protein transferase. The transferase catalyzes the addition of leucine, phenylalanine, or methionine to basic NH2-terminal residues of protein or peptide acceptors. It is reported here that the specific activities of the three enzymes coded for by the lactose operon are reduced in the mutant as compared to its parent and two spontaneous revertants, and that this reduction is most pronounced in cells grown with glucose as the carbon source. The results also indicate that when reduction occurs in the transferase-less mutant, percent activity of the lac operon enzymes progressively decreases, moving from the z gene (which codes for β -galactosidase) to the y gene (which codes for lac permease) to the a gene ( which codes for thiogalactoslde transacetylase). Because β-galactosidase and thiogalactoside transacetylase have been ruled out as potential substrates for the transferase, it is probable that the transferase acts on some protein involved in the overall control of transcription or translation of the lac operon. Mechanisms attempting to interpret the glucose and polarity effects in terms of a possible substrate for the transferase are discussed.