Detection and physical map of a omega tox+-related defective prophage in Corynebacterium diphtheriae Belfanti 1030(-)tox-

Abstract

A library of chromosomal DNA from Corynebacterium diphtheriae Belfanti 1030(-)tox- was cloned in the lambda phage vector EMBL4 and screened for sequences homologous to corynephage omega tox+ and the attB1-attB2 region of the C7(-)tox- chromosome. Two portions of the 1030(-)tox- chromosome, 35 and 30.5 kilobases long which contain, respectively, the entire region homologous to corynephage omega tox+ and the attB1-attB2 sites, were mapped with the restriction endonucleases BamHI and EcoRI. Chromosomal DNA from 1030(-)tox- was shown to contain a 15.5-kilobase region that was homologous to ca. 42% of the corynephage omega tox+ genome. These sequences were found to hybridize to three regions of the phage genome and do not contain either the diphtheria tox operon or the attP site. These sequences are distant from the chromosomal region that contains the attB1-attB2 sites. Moreover, unlike other known defective prophages, the physical map of this prophage starts at the cos site and is colinear with the vegetative phage map. The 30.5-kilobase region of the 1030(-)tox- chromosome, which contains the attB1-attB2 sites, has a central core region that is almost identical to the corresponding region of the C7(-)tox- chromosome; however, the flanking sequences in these two strains of C. diphtheriae are different.