Human cytomegalovirus origin of DNA replication (oriLyt) resides within a highly complex repetitive region

A global analysis of the 230-kilobase-pair (kbp) human cytomegalovirus genome revealed three regions that were very rich in repeated sequences. The region with the highest content of inverted and direct repeats lies between 92,100 and 93,500 bp, upstream of the gene encoding the single-stranded DNA binding protein. Cloned restriction fragments containing this region were able to replicate when trans-acting factors were provided by virus infection in a transient replication assay. With this assay, the region between 92,210 and 93,715 bp on the viral genome was defined as the minimal replication origin, oriLyt. The sequence composition and repeats within oriLyt were used to divide the region into two domains that may be important in origin function. Sequences flanking either the left or right side of the minimal oriLyt contributed to efficient replication; however, these sequences were not essential for origin function. Thus, the region of the viral genome with the most striking concentration of direct and inverted repeats corresponds to the oriLyt of human cytomegalovirus.