IMMEDIATE-EARLY PROTEIN BICP22 OF BOVINE HERPESVIRUS-1 TRANS-REPRESSES VIRAL PROMOTERS OF DIFFERENT KINETIC CLASSES AND IS ITSELF REGULATEDBY BICP0 AT TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL LEVELS

Bovine herpesvirus 1 (BHV-1) encodes four immediate-early (IE) protein s. The transactivators BICP0 and BICP4 are key regulatory elements in viral replication, and circ is a myristylated virion component, wherea s BICP22 - originating from a spliced 1.7-kb transcript synthesized wi th dual IE and late kinetics - has not yet been characterized as a pro tein. In this study, Western blot and immunofluorescence analysis usin g antisera against a C-terminal oligopeptide revealed major 50-kDa and minor 35-kDa species of BICP22, predominantly located in the nuclei o f BHV-1 infected cells. In transient expression assays, BICP22 acted a s transrepressor protein on viral promoters of different kinetic class es, e.g. the IE promoter of the BICP4/BICP0 gene, early promoter of th e BICP0 gene, and late promoter of the gC gene. The BICP22 gene promot er itself was not repressed by BICP22; it could be dissected into a pr oximal region stimulated by BICPO and a distal region stimulated by BH V-1 alpha-transinducing factor. Replacement of the BICP22 promoter by cytomegalovirus IE promoter revealed an additional posttranscriptional level of regulation whereby more BICP22 accumulated in cells when fun ctional BICPO was present. Interplay of BICP22 and BICPO might involve the recently described nuclear domains (ND10) and ubiquitin-dependent pathway.