Biotin interference assay of integrative recombination. Supercoiled
attP sites containing a single biotin dT substitution at one of the
indicated positions in the top strand (t.s.) were recombined with a
radiolabeled linear attB partner, and the recombination efficiency
was normalized to that of a control reaction with no substitutions
(10–20% recombination efficiency). Based on the x-ray crystal structure,
the biotin at -149 (*) is predicted to interfere with the putative
non-canonical Int binding in the same way that biotin at position -139 blocks
Int binding at P1. Biotin dT substitutions at positions -154, -149, and -144
required changing the wild-type sequences from A, C, and A, respectively; in
each case the unsubstituted control attP (wild-type (WT))
contained the identical changes.