The archaeal homolog of the Imp4 protein, a eukaryotic U3 snoRNP component

Homologs of the Imp4 protein, a component specific to the eukaryotic U3 sno RNP complex, have been found in all archaeal genomes. The archaeal and euka ryotic Imp4 proteins that are related to four other protein families, the I mp4-like, the SSF1 homologs and two sets of hypothetical proteins, are char acterized by the Imp4 signature pattern. These findings, together with the presence of other snoRNPs homologs in Archaea, provide evidence for similar RNA processing and folding in Eukarya and Archaea.