Deletion , Recombination and Gene Expression Involving the Bacteriophage 1 Attachment Site

I analyse illegitimate recombination events mediated by the bacteriophage h int gene by comparing the DNA sequences of a bacteriophage /\ hybrid containing the Saccharomyces cerewisiae (yeast) hid gene and five independently derived deletion mutants. Behaviours of these Ahis deletion mutants with respect to i&mediated recombination and to his3 gene expression are examined. Observations made are the following. (I ) Deletion break points in the yeast DNA occur only at sites that, have partial sequence homology to the core of the attachment site. (2) Deletion break points at the h attachment site occur at two or more distinct, locations within the common core, thus generating new hybrid core sequences. (3) In two instances. the recombination events generate unusual sequences at the crossover point. (4) Three deletions represent alternat,ive outcomes of recombination with the same yeast DNA sequence. (5) Phages differing only in hybrid core sequences behave quite differently in istmediated recombination and express his3 at different levels. Conclusions suggested from these observations are as follows. (1) II/ viva support for the idea that int protein produces staggered breaks in the attachment site core. (2) Sequences to the left of the core influence i&-mediated recombination. (3) DeleCons are formed by a break and join mechanism rather than by strand displacement. (4) The hybrid core regions can provide a Pribnow box that, when fused to appropriate sequences, forms a leftward promoter for his3 expression. (5) &t-mediated recombination produces a diversity of sequences at the novel joints that, have different functional consequences.