PTRF (polymerase I and transcript-release factor) is tissue-specific and interacts with the BFCOL1 (binding factor of a type-I collagen promoter) zinc-finger transcription factor which binds to the two mouse type-I collagen gene promoters

We have used the yeast two-hybrid system to clone the protein that interact s with the BFCOL1 (binding factor of a type-I collagen promoter) zinc-finge r transcription factor that was cloned previously as the factor that binds to the two mouse proximal promoters of the type-I collagen genes. We utiliz ed as bait the N-terminal domain of BFCOL1 that includes the zinc-finger DN A-binding domain. One cDNA contained a potential open reading frame for a p olypeptide of 392 amino acids and was identical to PTRF (polymerase I and t ranscript-release factor), which is involved in transcription termination o f the RNA polymerase I reaction. Northern-blot analysis revealed that the p attern of mRNA expression was similar to that of the type-I collagen gene. In addition, we detected the mRNA expression only in a fibroblast cell line and two bone cell lines, but not in other blood and neuronal cell lines. R ecombinant protein was shown to enhance the binding of BFCOL1 to its bindin g site in the mouse pro alpha 2(I) collagen proximal promoter in vitro. The transient-transfection experiment showed that PTRF had a suppressive effec t on the mouse pro alpha 2(I) collagen proximal promoter activity. We specu late that PTRF might play a role in the RNA polymerase II reaction as well as that of RNA polymerase I.