THE VP16 ACCESSORY PROTEIN HCF IS A FAMILY OF POLYPEPTIDES PROCESSED FROM A LARGE PRECURSOR PROTEIN

Upon lytic infection of permissive cells, the herpes simplex virus (HS V) transactivator protein VP16 associates with an accessory protein te rmed host cell factor (HCF). Binding to HCF activates VP16 for associa tion with the octamer motif-binding protein Oct-1, to form a multiprot ein-DNA complex responsible for activating transcription of the HSV im mediate early genes. We show that HCF comprises a series of related po lypeptides that range from 110 to 300 kd, all of which are encoded by a single gene. Although there is no obvious sequence similarity betwee n HCF and other known proteins, HCF contains eight repeats of a new 26 amino acid motif. cDNAs encoding HCF predict a large open reading fra me of 2035 codons. When expressed in human cells, this large open read ing frame encodes both the 300 kd and smaller HCF polypeptides, indica ting that the smaller polypeptides arise by processing of the 300 kd p rotein.