The interaction between virus and receptor is a process that mimics physiological ligand binding receptors and induces signal transduction. In the investigation of the interaction between HSV1 (Herpes Simplex virus 1) and human fibroblasts via virus binding to its receptor complex on cellular membranes, the HTRP (human transcription regulator protein), a protein encoded by an immediate-early gene of cellular response against the specific stimulation of HSV1 binding, was cloned from a cDNA library established from early gene response mRNA. The localization of HTRP expressed as a fusion polypeptide with a fluorescent protein in HeLa cells was confirmed to be the nucleus. The results of a yeast two-hybrid experiment indicated that HTRP is indeed involved in the interaction with the SAP (mSin3-associate polypeptide) complex via SAP30. A pull-down test and Western blotting in vitro, and immunoprecipitation in vivo also provided evidence in support of this result. The interaction of HTRP with SAP30 in its conserved domain implies that this protein family, as the products of immediate-early genes, comprise functional molecules involved in the transcriptional regulation of cells, which might be related to the inhibition of some cell survival genes.