THE ACTIVITY BINDING TO THE TERMINATION REGION OF SEVERAL POL-III GENES REPRESENTS A SEPARATE ENTITY AND IS DISTINCT FROM A NOVEL COMPONENTENHANCING U6 SNRNA TRANSCRIPTION

Human TFIIIC1, a basal transcription factor essentially required for e xpression of all pol III genes, exerts its function without primarily binding to DNA. We report here the purification of a termination site binding activity (TBA) which was initially described to be contained i n fractions designated as TFIIIC0. TEA specifically and strongly binds to the termination region of pol III genes with internal promoters an d can be completely separated from TFIIIC1 and a TFIIIC1 related activ ity (TFIIIC1-like), proving that DNA-binding of TEA is independent of these latter activites, Although TEA is not essentially required for, it strongly stimulates pol III transcription from intragenic promoters , This stimulation strictly depends on the presence of TFIIIC1 and is not observed in conjunction with TFIIIC1-like. We further present the identification of a novel activity, TFIIIU, which is also contained in crude fractions of TFIIIC0. TFIIIU can be separated from TEA by furth er purification and is essentially involved in transcription of the ma mmalian U6 gene. TFIIIU cannot be substituted for by any of the establ ished U6 transcription factors and thus represents a novel U6 transcri ption factor.