The UL9 ori-binding protein of herpes simplex virus 1: its expression and localization in vero cells

The ori-binding protein (OBP), an early protein which is encoded by the herpes simples virus 1 (HSV-1) UL9 gene and initiates the replication of viral DNA, was expressed in Escherichia coli, purified on an avidin resin and used for preparation of a mouse antiserum to OBP (OBP antiserum). Expression and localization of OBP in HSV-1-infected Vero cells was assessed by reverse transcription-polymerase chain reaction (RT-PCR) and indirect immunofluorescence test. RT-PCR revealed the presence of abundant UL9 transcripts from 3 to 12 hrs post infection (p.i). Traces of UL9 mRNA were detected already at 1.5 hr p.i. The OBP antiserum detected clumps of irregularly shaped structures in the nuclei of infected Vero cells first at 4 hrs p.i. These nuclear structures peaked at 5-6 hrs p.i. and later on (at 8-12 hrs p.i.) they changed into fine granules filling the whole nucleus.