Human transcription factor IIIC contains a polypeptide of 55 kDa specifically binding to Pol III genes

Human transcription factor IIIC contains a 55 kDa polypeptide which specifically interacts with the Adenovirus 2 VAI gene promoter and which mimics most of the DNA binding properties of the entire factor. The specificity and affinity of this protein:DNA interaction was demonstrated by: (i) Separation of purified fractions of hTFIIIC by SDS PAGE, electrotransfer to nitrocellulose, renaturation of proteins and their subsequent binding to the VAI gene, (ii) recovery and renaturation of proteins from SDS gels and identification of a fraction of hTFIIIC with a molecular mass less than 68 kDa, which specifically binds to VAI DNA, (iii) correlating the differential binding activity of the renatured 55 kDa component of hTFIIIC to mutated Pol III promoters with the ability of the entire factor to form functional transcription complexes thereon, and finally by (iv) specific crosslinking of the 55 kDa DNA binding component of hTFIIIC to the photoaffinity labeled B-box promoter sequence of the VAI gene.