A histone deacetylase inhibitor has been shown to induce differentiation of many cancer cells and senescence-like state of human fibroblasts. Previously, our data suggested that the region responsive to trichostatin A (TSA), a specific inhibitor of histone deacetylase, treatment in the p21(WAF1) promoter is located -100 bp upstream from transcription initiation site and contains a GC-box where both Sp1 and Sp3 are responsible. Here we show that another zinc-finger transcription factor, BFCOL1, which binds to the proximal pro alpha 2(I) collagen promoter, could also bind to this GC-box of the p21 promoter. In addition, we cloned a gene whose product interacts with this factor by yeast two-hybrid method. The cloned gene was a variant of GADD34 and lacking one PEST region. We found that this cDNA product decreased the DNA binding activity of BFCOL1 to the GC-rich region of p21 minimal promoter. (C) 1999 Academic Press.