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Polycistronic Effects of Catabolite Repression on the lac Operon

^a Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

ABSTRACT

The catabolite repression caused by glucose and glucose-6-phosphate has been studied for both ß-galactosidase and thiogalactoside transacetylase, the products of the operator proximal and distal cistrons of the lac operon, respectively. We find that both cistrons are affected coordinately by this form of repression. We also find that a single alteration at the lac promoter region is sufficient to abolish sensitivity to repression of both cistrons. From this, we conclude that there is only one target site for catabolite repression in the lac operon.

¹ Presently a post doctoral fellow of the Jane Coffin Childs Memorial Fund for Medical Research at the Department of Biological Sciences, Columbia University, New York, N.Y.