Stringent structural and sequence requirements of the human herpesvirus 6B lytic-phase origin of DNA replication

The lytic-phase origin of DNA replication from human herpesvirus 6B (HHV-6B oriLyt) contains two binding sites for the origin-binding protein (OBPH6B), both of which are required for DNA replication and which are separated by an AT-rich spacer. We have tested the functional significance of the structural, spatial and sequence charac-teristics of this spacer element by constructing a series of mutated origin sequences and analysing their replication efficiency. Changes in the sequence composition or length of the spacer resulted in dramatic decreases in replication efficiency. Fur-thermore, in contrast to what has been observed for herpes simplex virus type 1 (HSV-1) oriS, insertion of a complete helical turn of DNA into th