Molecular Identification and Characterization of hRPC11, the Smallest Subunit Specific for Human RNA Polymerase III

Full-length copies of cDNA of the hRPC11 gene encoding the smallest specific subunit of nuclear RNA polymerase III were identified among human transcripts with the use of the RT-PCR technique. The cloning of the first orthologue of the subunit RPC11 from a multicellular organism and the comparison of subunit hRPC11 of Homo sapiens (108 aa; M_r 12.3 kDa; pI 8.05) deduced from the cDNA primary structure with the homologous components of RNA polymerase III from Saccharomyces cerevisiae and Schizosaccharomyces pombe revealed the most important functional domains: a Zn-binding motif of the classic type (CxxCx_16-17CxxC) at the N-terminal region, and two extended regions of homology (KEVDDVLGG and RSADEPM) in the central and C-terminal parts of the molecule, respectively. The C-terminus of the RPC11 subunits is highly homologous to the unique zinc ribbon of the elongation factor TFIIS, which suggests a role for this subunit in the elongation or termination of RNA synthesis.