The increase in the number of subunits in eukaryotic RNA polymerase III relative to RNA polymerase II is due to the permanent recruitment of general transcription factors.
The number of subunits of RNA polymerases (RNAPs) increases during evolution from 5 in eubacteria to 12 in archaea. In eukaryotes, which have at least three RNAPs, the number of subunits has expanded from 12 in RNA polymerase II (RNAPII) to 14 in RNA polymerase I (RNAPI) and to 17 in RNA polymerase III (RNAPIII). It was recently demonstrated that the two additional subunits found in RNAPI relative to RNAPII are homologous to TFIIF, a dimeric general transcription factor of RNAPII. Here, we extend this finding by demonstrating that four of the five RNAPIII-specific subunits are also homologous to transcription factors of RNAPII. We use the available evidence to propose an evolutionary history of the eukaryotic RNAPs and argue that the increases in the number of subunits that occurred in RNAPs I and III are due to the permanent recruitment of preexisting transcription factors.
Carter
Robert
R
Département de biologie Université d'Ottawa, Ottawa, Ontario, Canada.
Drouin
Guy
G
D000595:Amino Acid Sequence; D056890:Eukaryota / Q000201:enzymology*; D019143:Evolution, Molecular; D006801:Humans; D008957:Models, Genetic; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism*; D012320:RNA Polymerase III / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D048229:Sulfolobus solfataricus / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D019473:Transcription Factors, TFII / Q000737:chemistry / Q000378:metabolism
D021122:Protein Subunits; D014157:Transcription Factors; D019473:Transcription Factors, TFII; C066644:transcription factor TFIIE; D012319:RNA Polymerase II; D012320:RNA Polymerase III; C056604:transcription factor TFIIF