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The Time Required for cro Gene Product to Establish Dominance in Coliphage Lambda Lysogens

Department of Biology The Chinese University of Hong Kong, Shatin, N.T., Hong Kong

To measure the length of heating required to convert a lysogen in the immune (im⁺) phase into the anti-immune (im^-) phase, rex gene activity was used as an indicator. It was observed that 5 min heating at 41 °C did not shift any lysogenic cells of 594(N^-cI857O^-) from the im⁺ phase into the im^- phase, and it took 17 min heating at 41 °C followed by long hours of culture at 30 °C to shift half of the lysogenic cells into the im^- phase. Such a length of heating is too long to be accounted for by blocking of the expression of lambda repressor by cro gene product. The result is more consistent with accumulation of a certain level of cro gene product during heating so that the synthesis of the repressor is blocked even after a return to low temperature.

Keywords: phage, cro gene, immunity, regulation

Received 8 May 1981; accepted 5 October 1981.