Rates of flagellar- and P1 infective-phase variation by three site-specific recombinase genes in every possible combination.

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Abstract
Rates of flagellar and P1 infective-phase variation, caused by reversible inversion of an H(= PD) and a C segment, respectively, were examined with strains having the three site-specific recombinase, genes, hin+, pin+, and cin+, in every possible combination. The variation rates were compared in terms of gene functions on the assumptions that the three genes are similar in gene dosage and comparable with one another in the amount of gene products and that each rate reflects an activity of a single gene or genes combined. The three genes were arranged in the order of the variation rate they caused: cin+ > hin+ > pin+ for both directions of H inversion, cin+ .mchgt. hin+ > pin+ for C(+) inversion, and cin+ .mchgt. pin+ > hin+ for C(-) inversion. For C inversion the rates in a cin+ strain were higher than those in hin+ and pin+ by two or three orders of magnitude. It was suggested that for H inversion two couples of the genes, hin+ and pin+ and pin+ and cin+, function together, but hin+ and cin+ interact against each other and that for C inversion hin+ and pin+ interact synergistically, but function against cin+. The variation of P1 cin+ reached equilibrium at a ratio of C(+)/C(-) = 6.1/3.9 in the four kinds of lysogenic strains, and the generations bringing about the equilibrium ranged from 16 to 36 depending on the host gene(s) that function against cin+.