Sequence of terminal regions of cowpox virus DNA: arrangement of repeated and unique sequence elements.

One terminal EcoRI fragment of the genome of cowpox virus (CPV) strain Brighton red has been cloned in plasmid pBR325, and the nucleotide sequence of the 2,725-base-pair Sal I fragment corresponding to that at the end of the viral genome has been determined. The fragment consists of three unique sequence regions flanking two sets of repeated sequence. The repeated sequence sets are composed of four types of subunits, the majority of which are arranged in higher-order repeat units. The subunits are themselves closely related; two are subsets of a third, whereas the fourth is a recombinant of the first two. The fragment possesses no long open reading frames (maximal coding potential, 65 amino acids). The sequence of this CPV DNA Sal I fragment is compared with that of the corresponding fragment of vaccinia virus WR DNA [Baroudy, B. M., Venkatesan, S. & Moss, B. (1982) Cell 28, 315-324; Venkatesan, S., Baroudy, B. M. & Moss, B. (1981) Cell 25, 805-813]. Two of the unique sequence regions of the two viruses are related to the extent of 96%, and the third contains at least one sequence of 112 residues that is 98% homologous. As for the repeated sequence sets, those of vaccinia virus are composed of only two, rather than four, types of subunit, one of which is identical to one of the CPV subunits, whereas the other differs from another CPV subunit by only three mismatches and one deletion. However, the arrangement of subunits in the two viruses is different, that in vaccinia virus DNA being simpler. Both subunits as well as repeat units probably arose as a result of unequal crossover.