Abstract
Although most of the key components of the transcription apparatus, and in particular, RNA polymerase (RNAP) subunits, are conserved between archaea and eukaryotes, no archaeal homologs of the small RPB8 subunit of eukaryotic RNAP have been detected. We report that orthologs of RPB8 are encoded in all sequenced genomes of hyperthermophilic Crenarchaeota and a recently sequenced "korarchaeal" genome, but not in Euryarchaeota or the mesophilic crenarchaeon Cenarchaeum symbiosum. These findings suggest that all 12 core subunits of eukaryotic RNAPs were already present in the last common ancestor of the extant archaea.This article was reviewed by Purificacion Lopez-Garcia and Chris Ponting.
Highlights
The heteromultimeric eukaryotic RNA polymerase (RNAP) consist of 12 subunits (Rpb1–12), of which 11 are conserved in archaea and eukaryotes whereas one, Rpb8, is thought to be unique for eukaryotes [1,2,3,4,5,6]
The two structures are in good agreement and indicate that Rpb8 forms a distinct version of the OB(oligonucleotide-oligosaccharide-binding) fold [9] that is characterized by a distinct pattern of 9 β-strands and a pair of invariant glycines in the turn between strands 7 and 8
Rpb8 genetically interacts with another small subunit, Rpb6, that is adjacent to the pore module in the core RNAP structure [6]
Summary
Rpb8 is a small protein that typically consists of ~120–150 amino acids and shows relatively poor sequence conservation in eukaryotes. In the course of the genome annotation for the first sequenced member of the "Korarchaeota", a putative deep branch of archaea ([10] and manuscript in preparation), one of us (JGE) identified a short (110 amino acids) predicted protein for which some of the best hits in a BLAST search [11] were the eukaryotic Rpb8 subunits.
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