Research Article 11: Deletion of Translational Start Signals in the lac Operon of E. coli

Abstract

The order of genetic elements in the lac operon of E. coli is p-o-z-y-a (Miller, Ippen, Scaife, and Beckwith, 1968), where p, the promoter, is the region of initiation of transcription of the operon; o, the operator, is the site of action of the lac repressor; and z, y, and a are structural genes coding for the proteins β-galactosidase, permease or M-protein and thiogalactoside transacetylase, respectively. The nearby i gene, codes for the structure of the repressor protein. Since transcription begins in the promoter region, it seems likely that the operator is transcribed as part of the lac mRNA. However, evidence has been presented that the operator is not translated as part of the first structural gene, z, and it is possible that the operator is not translated at all (Reznikoff and Beckwith, 1969; Bhorjee, Fowler, and Zabin, 1969). If this is so, then translation of the operon mRNA would begin at the z gene. It may be asked, then, whether there is a special translation start signal at the beginning of the z gene-copy in the mRNA which is different from internal start signals or whether the signals at the beginning of z, y and a are identical. In this paper, we present evidence that there is no such site in the o-z boundary region which is essential for operon expression.

Previous results suggested the existence of a region essential to the expression of the lac operon lying between (or including the end of) the operator and the beginning...