We have screened a human cDNA expression library with a digoxygenin-labelle
d protein phosphatase 1 (PP1) probe to identify novel PP1 interacting prote
ins. Eleven cDNA clones were isolated, which included genes encoding two pr
eviously characterised and six novel PP1 binding proteins. Three of the cDN
As encoded a protein called host cell factor (HCF), which is an essential c
omponent of the cellular complex required for the transcription of the herp
es simplex virus (HSV) immediate-early (IE) genes. We demonstrate that HCF
and PP1 exist as a complex in nuclear extracts and that this complex is dis
tinct from the form of HCF that associates with HSV VP16, The data suggest
novel roles for HCF and PP1, which may be relevant to their functions in tr
anscription and cell cycle progression.