Cloning and characterization of two evolutionarily conserved subunits (TFIIIC102 and TFIIIC63) of human TFIIIC and their involvement in functional interactions with TFIIIB and RNA polymerase III

Human transcription factor IIIC (hTFIIIC) is a multisubunit complex that me diates transcription of class III genes through direct recognition of promo ters (for tRNA and virus-associated RNA genes) or promoter-TFIIIA complexes (for the 5S RNA gene) and subsequent recruitment of TFIIIB and RNA polymer ase III. We describe the cognate cDNA cloning and characterization of two s ubunits (hTFIIIC63 and hTFIIIC102) that are present within a DNA-binding su bcomplex (TFIIIC2) of TFIIIC and are related in structure and function to t wo yeast TFIIIC subunits (yTFIIIC95 and yTFIIIC131) previously shown to int eract, respectively, with the promoter (A box) and with a subunit of yeast TFIIIB. hTFIIIC63 and hTFIIIC102 show parallel in vitro interactions with t he homologous human TFIIIB and RNA polymerase III components, as well as ad ditional interactions that may facilitate both TFIIIB and RNA polymerase II I recruitment. These include novel interactions of hTFIIIC63 with hTFIIIC10 2, with hTFIIIB90, and with hRPC62, in addition to the hTFIIIC102- hTFIIIB9 0 and hTFIIIB90-hRPC39 interactions that parallel the previously described interactions in yeast. As reported for yTFIIIC131, hTFIIIC102 contains acid ic and basic regions, tetratricopeptide repeats (TPRs), and a helix-loop-he lix domain, and mutagenesis studies have implicated the TPRs in interaction s both with hTFIIIC63 and with hTFIIIB90. These observations further docume nt conservation from yeast to human of the structure and function of the RN A polymerase III transcription machinery, but in addition, they provide new insights into the function of hTFIIIC and suggest direct involvement in re cruitment of both TFIIIB and RNA polymerase III.