eukaryotic RNA polymerase Rpo8; evolutionary origin; Asgard archaea; function conservation.

Here, we identified 141 archaeal rpo8 orthologs restrictively in TACK and Asgard archaea superphyla among 617 high-quality archaeal metagenome-assembled genomes. Phylogenetically the Asgard and eukaryotic Rpo8s clustered a well-supported sister clade; and an Asgard Rpo8 interacted with the yeast Rpb1 via conserved GGLLM motif in vitro.

While heterogenous expression of any Asgard and TACK rpo8s was lethal to an euryarchaeon, hinting its acquisition via horizontal gene transfer instead of vertical inheritance. Knockout of the yeast rpo8 just reduced the transcription efficiency and physiological fitness particularly in stress tolerance, while an Asgard Rpo8 was capable to complement the function of the yeast homolog. Multi-omic analysis found that Rpo8 acted equivalently in the three yeast RNAPs, and its vacant also reduced rRNA transcription, so hindered ribosome biogenesis determined by size exclution chromatography, and lower translation assayed via polysome profiling.