Integration of the related prophages lambda, phi 80 and their hybrid lambda att80 into the secondary chromosomal att sites of wild-type Escherichia coli

The family of lambdoid phages displays a varying specificity of integration into the host chromosome. The lambda phage DNA failed to get inserted at the secondary attachment site(s) of the gal operon (frequency less than 2.6 X 10(-8)) in the presence of the primary (normal) one. By contrast, phi 80 and the lambda att80 hybrid integrated into wild-type Escherichia coli at least, at two secondary att sites of the btuB locus, the latter phage being also capable of integration in the vicinity of purE and purC (frequency 2 X 10(-3) to 10(-4)). Integration of phi 80 and lambda att80 into btuB occurred with about the same frequency as in cells deleted for normal insertion site (0.7 divided by 4.0 X 10(-6)). An analysis of the secondary lysogens with the prophage in btuB showed them to be polylysogens; the additional prophage(s) was found in the primary att site. We also failed to observe integration of phi 80 and lambda att80 with formation of secondary monolysogens into other foci (frequency less than 0.0035, if multiplicity of infection was 10(-3) or 10). It is presumed that phi 80 and lambda att80 prophages get only integrated at secondary att sites in case the primary site is occupied.