Abstract
One conceivable function for constitutive integrase formation by lambda prophage is to stabilize the inserted state by catalyzing reinsertion of prophages that are accidentally excised. As this hypothesis implies a dynamic equilibrium betwen inserted and noninserted DNA, the existence of such an equilibrium is explored. By examining the frequency with which prophages appear in an initially unoccupied chromosomal site of a lysogenic bacterium in which the prophage attachment site is duplicated, the off-rate is estimated as less than 10(-2) per generation for wild-type lambda, and less than 4 x 10(-4) for N- mutants of lambda. From the rate of integrase-catalyzed haploidization of certain partial diploid strains, the rate of spontaneous integrase activity is estimated as 3 x 10(-3) per generation. From these values I conclude that constitutive integrase will not appreciably stabilize the inserted state by virtue of its known activity.
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Selected References
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