The Roseolovirus genus of the Betaherpesvirinae consists of the very closely related viruses, human herpesvirus 6 variants A and B (HHV-6A and HHV-6B) plus the somewhat more distantly related human herpesvirus 7 (HHV-7). The roseoloviruses each encode a homolog of the alphaherpesvirus origin binding protein (OBP) which is required for lytic DNA replication. In contrast, members of the other betaherpesvirus genera, the cytomegaloviruses, initiate DNA replication by a different mechanism. To better understand the basis of roseolovirus OBP sequence specificity, we investigated their ability to recognize each other's binding sites. HHV-6A OBP (OBP(H6A)) and HHV-6B OBP (OBP(H6B)) each bind to both of the HHV-7 OBP sites (OBP-1 and OBP-2) with similar strengths, which are also similar to their nearly equivalent interactions with their own sites. In contrast, HHV-7 OBP (OBP(H7)) had a gradient of binding preferences: HHV-7 OBP-2 > HHV-6 OBP-2 > HHV-7 OBP-1 > HHV-6 OBP-1. Thus, the roseolovirus OBPs are not equally reciprocal in their recognition of each other's OBP sites, suggesting that the sequence requirements for the interaction of OBPH7 at the OBP sites in its cognate oriLyt differ from those of OBPH6A and OBPH6B.
Copyright 2001 Academic Press.