Protein-protein interactions between human exosome components support the assembly of RNase PH-type subunits into a six-membered PNPase-like ring.
The exosome is a complex of 3'-->5' exoribonucleases, which functions in a variety of cellular processes, all requiring the processing or degradation of RNA. Here we present a model for the assembly of the six human RNase PH-like exosome subunits into a hexameric ring structure. In part, this structure is on the basis of the evolutionarily related bacterial degradosome, the core of which consists of three copies of the PNPase protein, each containing two RNase PH domains. In our model three additional exosome subunits, which contain S1 RNA-binding domains, are positioned on the outer surface of this ring. Evidence for this model was obtained by the identification of protein-protein interactions between individual exosome subunits in a mammalian two-hybrid system. In addition, the results of co-immunoprecipitation assays indicate that at least two copies of hRrp4p and hRrp41p are associated with a single exosome, suggesting that at least two of these ring structures are present in this complex. Finally, the identification of a human gene encoding the putative human counterpart of the bacterial PNPase protein is described, which suggests that the exosome is not the eukaryotic equivalent of the bacterial degradosome, although they do share similar functional activities.
Raijmakers
Reinout
R
Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands.
Egberts
Wilma Vree
WV
van Venrooij
Walther J
WJ
Pruijn
Ger J M
GJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D019556:COS Cells; D002460:Cell Line; D003001:Cloning, Molecular; D019295:Computational Biology; D005089:Exocytosis; D005095:Exoribonucleases / Q000737:chemistry*; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D011117:Polyribonucleotide Nucleotidyltransferase / Q000737:chemistry* / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D020798:Two-Hybrid System Techniques
D021122:Protein Subunits; C056502:ribonuclease PH; D011117:Polyribonucleotide Nucleotidyltransferase; D005095:Exoribonucleases