Summary
We have constructed and tested three lac diploid strains in an attempt to show whether operator-constitutive mutations relieve catabolite repression of the lac operon. Each of these carries a different operator mutation on the chromosome, and all three have the genotype I+P+OcZ+Y-polar/F′lac I+P+O+ZdelY+A+. When these strains were grown in medium containing glucose plus gluconate, synthesis of β-galactosidase (directed by a gene cis to a mutant operator) and of thiogalactoside transacetylase (directed by a gene cis to an intact operator) suffered equal catabolite repression. We conclude that the operator-constitutive mutations have no effect on catabolite repression. Since it has been shown in analogous experiments that all promoter mutations tested do alleviate catabolite repression, these results are consistent with the view that the operator and promoter are functionally distinct.
Similar content being viewed by others
References
Arditti, R. R., Scaife, J. G., Beckwith, J. R.: The nature of mutants in the lac promoter region. J. molec. Biol. 38, 421 (1968).
Crombrugghe, B. de, Chen, B., Anderson, W., Nissley, P., Gottesman, M., Pastan, I.: Lac DNA, RNA polymerase and cyclic AMP receptor protein, cyclic AMP, lac repressor and inducer are the essential elements for controlled lac transcription. Nature new Biol. 231, 139 (1971).
Davies, J. E., Jacob, F.: Genetic mapping of the regulator and operator genes of the lac operon. J. molec. Biol. 36, 413 (1968).
Gilbert, W., Müller-Hill, B.: The lac operator is DNA. Proc. nat. Acad. Sci. (Wash.) 58, 2415 (1967).
Jacob, F., Monod, J.: Genetic regulatory mechanisms in the synthesis of protein. J. molec. Biol. 3, 318 (1961).
Miller, J. H., Ippen, K., Scaife, J. G., Beckwith, J. R.: The promoter-operator region of the lac operon of Escherichia coli. J. molec. Biol. 38, 413 (1968).
Myers, G. L., Sadler, J. R.: Mutational inversion of control of the lactose operon of Escherichia coli. J. molec. Biol. 58, 1 (1971).
Riggs, A. D., Bourgeois, S., Newby, R. F., Cohn, M.: DNA binding of the lac repressor. J. molec. Biol. 34, 365 (1968).
Scaife, J. G., Beckwith, J. R.: Mutational alteration of the maximal level of lac operon expression. Cold Spr. Harb. Symp. quant. Biol. 31, 403 (1966).
Silverstone, A. E., Magasanik, B., Reznikoff, W. S., Miller, J. H., Beckwith, J. R.: Catabolite sensitive site of the lac operon. Nature (Lond.) 221, 1012 (1969).
Smith, T. F., Sadler, J. R.: The nature of lactose operator constitutive mutations. J. molec. Biol. 59, 273 (1971).
Yudkin, M. D.: Catabolite repression of the lac operon: the contribution of transcriptional repression. Biochem. J. 114, 307 (1969a).
—: Catabolite repression of the lac operon: separate repression of two enzymes. Biochem. J. 114, 313 (1969b).
—: Catabolite repression of the lac operon: effect of mutations in the lac promoter. Biochem. J. 118, 741 (1970).
—: Effect of point mutations in the lac promoter on transient and severe catabolite repression of the lac operon of Escherichia coli. Biochem. J. 123, 579 (1971).
Author information
Authors and Affiliations
Additional information
Communicated by P. Starlinger
Rights and permissions
About this article
Cite this article
Yudkin, M.D., Reddy, S. Catabolite repression of the Lac operon: Effect of operator-constitutive mutations. Molec. Gen. Genet. 113, 297–301 (1971). https://doi.org/10.1007/BF00272329
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00272329