Abstract
1. Catabolite repression of β-galactosidase and of thiogalactoside transacetylase was studied in several strains of Escherichia coli K 12, in an attempt to show whether a single site within the structural genes of the lac operon co-ordinately controls translational repression for the two enzymes. In all experiments the rate of synthesis of the enzymes was compared in glycerol–minimal medium and in glucose–minimal medium. 2. In a wild-type strain, glucose repressed the synthesis of the two enzymes equally. 3. The possibility that repression was co-ordinate was investigated by studies of mutant strains that carry deletions in the genes for β-galactosidase or galactoside permease or both. In all of the strains with deletions, the repression of thiogalactoside transacetylase persisted, and it is concluded that there is no part of the structural gene for β-galactosidase that is essential for catabolite repression of thiogalactoside transacetylase. 4. Subculture of one strain through several transfers in rich medium greatly increased its susceptibility to catabolite repression by glucose. It is concluded that unknown features of the genotype can markedly affect sensitivity to catabolite repression. 5. These results make it clear that one cannot draw valid conclusions about the effect of known genotypic differences on catabolite repression from a comparison of two separate strains; to study the effect of a particular genetic change in a lac operon it is necessary to construct a partially diploid strain so that catabolite repression suffered by one lac operon can be compared with that suffered by another. 6. Four such partial diploids were constructed. In all of them catabolite repression of β-galactosidase synthesized by one operon was equal in extent to catabolite repression of thiogalactoside transacetylase synthesized by the other. 7. Taken together, these results suggest that catabolite repression of β-galactosidase and thiogalactoside transacetylase is separate but equal.
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- COHN M., HORIBATA K. Physiology of the inhibition by glucose of the induced synthesis of the beta-galactosideenzyme system of Escherichia coli. J Bacteriol. 1959 Nov;78:624–635. doi: 10.1128/jb.78.5.624-635.1959. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Grodzicker T., Zipser D. A mutation which creates a new site for the re-initiation of polypeptide synthesis in the z gene of the lac operon of Escherichia coli. J Mol Biol. 1968 Dec;38(3):305–314. doi: 10.1016/0022-2836(68)90388-4. [DOI] [PubMed] [Google Scholar]
- Malamy M. H. Frameshift mutations in the lactose operon of E. coli. Cold Spring Harb Symp Quant Biol. 1966;31:189–201. doi: 10.1101/sqb.1966.031.01.027. [DOI] [PubMed] [Google Scholar]
- Moses V., Yudkin M. D. Catabolite repression in Escherichia coli. A study of two hypotheses. Biochem J. 1968 Nov;110(1):135–142. doi: 10.1042/bj1100135. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Newton W. A., Beckwith J. R., Zipser D., Brenner S. Nonsense mutants and polarity in the lac operon of Escherichia coli. J Mol Biol. 1965 Nov;14(1):290–296. doi: 10.1016/s0022-2836(65)80250-9. [DOI] [PubMed] [Google Scholar]
- Yudkin M. D. Catabolite repression of the lac operon. The contribution f trascriptional repression. Biochem J. 1969 Sep;114(2):307–311. doi: 10.1042/bj1140307. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Yudkin M. D., Moses V. Carabolite repression of the lac operon. Repression of translation. Biochem J. 1969 Jun;113(2):423–428. doi: 10.1042/bj1130423. [DOI] [PMC free article] [PubMed] [Google Scholar]