Similarities in transcription factor IIIC subunits that bind to the posterior regions of internal promoters for RNA polymerase III.
BACKGROUND
In eukaryotes, RNA polymerase III (RNAP III) transcribes the genes for small RNAs like tRNAs, 5S rRNA, and several viral RNAs, and short interspersed repetitive elements (SINEs). The genes for these RNAs and SINEs have internal promoters that consist of two regions. These two regions are called the A and B blocks. The multisubunit transcription factor TFIIIC is required for transcription initiation of RNAP III; in transcription of tRNAs, the B-block binding subunit of TFIIIC recognizes a promoter. Although internal promoter sequences are conserved in eukaryotes, no evidence of homology between the B-block binding subunits of vertebrates and yeasts has been reported previously.


RESULTS
Here, I reported the results of PSI-BLAST searches using the B-block binding subunits of human and Shizosacchromyces pombe as queries, showing that the same Arabidopsis proteins were hit with low E-values in both searches. Comparison of the convergent iterative alignments obtained by these PSI-BLAST searches revealed that the vertebrate, yeast, and Arabidopsis proteins have similarities in their N-terminal one-third regions. In these regions, there were three domains with conserved sequence similarities, one located in the N-terminal end region. The N-terminal end region of the B-block binding subunit of Saccharomyces cerevisiae is tentatively identified as a HMG box, which is the DNA binding motif. Although I compared the alignment of the N-terminal end regions of the B-block binding subunits, and their homologs, with that of the HMG boxes, it is not clear whether they are related.


CONCLUSIONS
Molecular phylogenetic analyses using the small subunit rRNA and ubiquitous proteins like actin and alpha-tubulin, show that fungi are more closely related to animals than either is to plants. Interestingly, the results obtained in this study show that, with respect to the B-block binding subunits of TFIIICs, animals appear to be evolutionarily closer to plants than to fungi.
Division of Microbiology, National Institute of Health Sciences, Setagaya-ku, Tokyo 158-8501, Japan. sachiko@nihs.go.jp
Sachiko
S
Matsutani
D000595:Amino Acid Sequence; D000818:Animals; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D005075:Biological Evolution; D005658:Fungi / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007313:Insecta / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D010944:Plants / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D012320:RNA Polymerase III / Q000235:genetics*; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D019474:Transcription Factors, TFIII / Q000737:chemistry* / Q000378:metabolism; D014714:Vertebrates / Q000235:genetics / Q000378:metabolism*; D000098832:Transcription Factor TFIIIC
D029681:Arabidopsis Proteins; D021122:Protein Subunits; D029702:Schizosaccharomyces pombe Proteins; D019474:Transcription Factors, TFIII; D000098832:Transcription Factor TFIIIC; D012320:RNA Polymerase III