MOLECULAR CHARACTERIZATION OF THE GENES INVOLVED IN O-ANTIGEN MODIFICATION, ATTACHMENT, INTEGRATION AND EXCISION IN SHIGELLA-FLEXNERI BACTERIOPHAGE-SFV

Bacteriophage SN is a temperate phage of Shigella flexneri responsible for converting serotype Y (3,4) to serotype 5a (V; 3,4) through its g lucosyl transferase gene. The glucosyl transferase (gtr) gene of SfV h as been cloned and shown to partially convert S. flexneri serotype Y t o serotype 5a. In this study, we found that the serotype-converting re gion of SfV was approximately 2.5 kb in length containing three contin uous ORFs. The recombinant strain carrying the three complete ORFs exp ressed the type V and group antigen 3,4, both indistinguishable from t hat of S. flexneri 5a wild-type strain. The interruption of orf5 or or f6 gave partial conversion in the S. flexneri recombinant strain indic ated by the incomplete replacement of group antigen 3,4. The region ad jacent to the serotype-conversion genes was found to be identical to t he attP-int-xis region of phage P22. Altogether, an approximately 2.2- kb sequence covering a portion of the serotype-conversion (approximate ly 500 nt)-attP-int-xis regions of SfV was remarkably similar to that of P22. (C) 1997 Elsevier Science B.V.