Table of Contents
International Journal of Evolutionary Biology
Volume 2014, Article ID 609865, 11 pages
Research Article

Evolution of the B-Block Binding Subunit of TFIIIC That Binds to the Internal Promoter for RNA Polymerase III

Division of Microbiology, National Institute of Health Sciences, Tokyo 158-8501, Japan

Received 11 October 2013; Revised 17 December 2013; Accepted 19 December 2013; Published 12 February 2014

Academic Editor: Andres Moya

Copyright © 2014 Sachiko Matsutani. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Eukaryotic RNA polymerase III transcribes tRNA genes, and this requires the transcription factor TFIIIC. Promoters are within genes, with which the B-block binding subunit of TFIIIC associates to initiate transcription. The binding subunits are more than 1000 amino acids in length in various eukaryotic species. There are four regions with conserved sequence similarities in the subunits. The helix-turn-helix motif is included in one of these regions and has been characterized as the B-block_TFIIIC family in the Pfam database. In the NCBI and EMBL translated protein databases, there are archaeal proteins (approximately 100 amino acids in length) referred to as B-block binding subunits. Most of them contain a B-block_TFIIIC motif. DELTA-BLAST searches using these archaeal proteins as queries showed significant multiple blast hits for many eukaryotic B-block binding subunits on the same proteins. This result suggests that eukaryotic B-block binding subunits were constituted by repeating a small unit of B-block_TFIIIC over a long evolutionary period. Bacterial proteins have also been annotated as B-block binding subunits in the databases. Here, some of them were confirmed to have significant similarities to B-block_TFIIIC. These results may imply that part of the RNAP III transcription machinery existed in the common ancestry of prokaryotes and eukaryotes.