Analysis of an origin of DNA replication located at the L terminus of the genome of pseudorabies virus.

We have localized an origin of DNA replication at the L terminus of the pseudorabies virus genome. This origin differs in location as well as in general structure from the origins of replication of other herpesviruses that have been identified. The 600 leftmost nucleotides of the genome that were found to include origin function have been analyzed. This sequence is composed of an 82-bp palindrome whose center of symmetry is separated by 352 unique bp (UL2). Within the UL2, a sequence that fits the consensus sequence of the NF1 binding site, as well as one that has partial homology to the binding site of UL9 of herpes simplex virus, is present. Using truncated fragments of DNA, sequences essential for minimal origin function were delimited to within a fragment that includes the terminal 104 bp of the left end of the genome. Within these 104 bp, two elements essential to origin function have been identified. One of these elements is present within the terminal 64 bp of the L component (within one of the palindromic arms). The other is present within the 22 bp of the UL2 adjacent to this palindromic arm. Other auxiliary elements, although not essential for origin function, contribute to more efficient replication. The NF1 and UL9 binding site homologies were found to be nonessential to origin function.