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Control of Expression of the L-Arabinose Operon in Temperature-Sensitive Mutants of Gene araC in Escherichia coli B/r

^a Department of Biological Sciences, University of California at Santa Barbara, Santa Barbara, California 93106

ABSTRACT

Expression of the L-arabinose operon in Escherichia coli B/r is dependent on the temperature of growth of the araC mutants reported in this paper. Analysis of these temperature-sensitive regulatory mutants indicates that both repressor and activator activities are thermolabile. The simplest model to explain the manner in which the operon is controlled is one suggesting that the regulatory gene, araC, codes for a protein which upon synthesis acts as a repressor molecule and prevents operon function. When inducer is added, the repressor undergoes a conformational shift and becomes an activator which switches on enzyme synthesis, provided the repressor concentration is reduced to a sufficiently low level in the cell. These data lend strong support to the model that both activities are the result of the same gene product.

¹ Present address: Biology Department, Marquette University, Milwaukee, Wis. 53233.