Identification and characterization of a second putative origin of DNA replication in a baculovirus of Orgyia pseudotsugata.

A 7.5-kb region (96.8-2.5 m.u.), called Op5, of the Orgyia pseudotsugata multinucleocapsid nuclear polyhedrosis virus (OpMNPV) genome that contains an origin of DNA replication was characterized. This region replicates several times more efficiently and is unrelated to the previously identified putative origin of replication located on the viral HindIII-N fragment. In contrast to HindIII-N, the origin on Op5 contains repeated sequences with limited sequence identity to the homologous regions from AcMNPV. In isolation, these repeated sequences were not sufficient for origin activity in OpMNPV-infected Lymantria dispar cells, but required an additional 1.3 kb of sequences located to the left of the repeats. Four regions of the OpMNPV genome that crosshybridize with the repeated region were also found to replicate in our infection-dependent DNA replication assay. A deletion clone of Op5 that replicates efficiently in OpMNPV-infected L. dispar cells, was found to replicate at less than 2% the replication level of AcMNPV hr2 in AcMNPV-infected Spodoptera frugiperda cells.