Analysis of TFIIH subunit through isolation of the gene from Schizosaccharomyces pombe corresponding to that of Saccharomyces cerevisiae SSL1, reveals the presence of conserved structural motifs.

We isolated a Schizosaccharomyces pombe (Sz. pombe) gene encoding the counterpart of the TFIIH subunit Homo sapiens (H. sapiens) p44 and Saccharomyces cerevisiae (S. cerevisiae) SSL1, and we named this gene product p47. Contrary to the case of SSL1, which is an essential gene of S. cerevisiae, p47 is not essential for the viability of Sz. pombe. The deduced amino acid sequence revealed that this TFIIH subunit is highly conserved during evolution. Comparison of the primary structures revealed differences in the predicted positions of introns in the Caenorhabditis elegans (C. elegans) gene encoding the p47 counterpart found during the genome project. A charged cluster in the N-terminal region is present in the two yeasts. Two putative zinc-binding motifs, an extended C2H2 zinc finger with a 'C8 motif' and a second putative zinc-binding motif common to the two TFIIH subunits, were also found, the former being completely conserved. The latter motif consists of five cysteine residues and is also present in hp44, SSL1 and another TFIIH subunit, human p34 (hp34). Since one zinc atom can bind to four ligands in zinc-binding motifs, the conservation of cysteine residues was given attention. This motif is completely conserved in p47 homologues derived from the four species. As one cysteine residue is not conserved among the homologues of hp34, the consensus of this motif is concluded to be Cys X2-Cys-X(10,12)-Cys-X2-Cys. This nucleotide sequence has been deposited in the GenBank Data Library under Accession Number AF017646.