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. Author manuscript; available in PMC: 2011 Jul 18.
Published in final edited form as: Adv Exp Med Biol. 2010;702:9–28.

Figure 1. Schematics of domains in ‘exosomes’ from bacteria, archaea, and eukaryotes.

Figure 1

A) Bacterial RNase PH and PNPase subunits. Bacterial RNase PH contains a 3′ to 5′ phosphorolytic exoribonucleolytic active site (red circle). Bacterial PNPase contains five domains: RNase PH 1, the alpha domain, RNase PH 2, a KH domain, and an S1 domain. A 3′ to 5′ phosphorolytic exoribonucleolytic active site resides in the RNase PH 2 domain (red circle). B) Archaeal exosome subunits. Archaeal exosomes include four subunits: Rrp41, that contains a RNase PH 2-like domain with a 3′ to 5′ phosphorolytic exoribonucleolytic active site (red circle), Rrp42, that contains a RNase PH 1-like domain, and either Csl4 or Rrp4. Csl4 contains an N-Terminal Domain (NTD), a S1 domain, and a KH domain. Rrp4 contains an N-Terminal Domain (NTD), a S1 domain, and a Carboxy Terminal Domain (CTD). C) Eukaryotic exosome subunits. Protozoan and metazoan exosomes contain either ten or eleven components consisting of nine catalytically inert core components (Rrp41, Rrp42, Mtr3, Rrp43, Rrp46, Rrp45, Csl4, Rrp4, and Rrp40) and two active components Rrp44 and Rrp6. Alternative names for each of the eukaryotic subunits are included. Rrp44 contains five annotated domains: a PIN (PIlus N terminal) domain with a Cysteine-Rich sequence (CR3), two Cold Shock Domains (CSD1 and CSD2), a Ribo Nuclease Binding (RNB) domain, and an S1 domain. The “hydrolytic” endoribonucleolytic activity is located within the PIN domain (yellow circle), and the processive 3′ to 5′ hydrolytic exoribonucleolytic activity resides in the RNB domain (green circle). Metazoan exosomes may vary in their utilization of Rrp44 (e.g. three in human H1, H2, and H3). Rrp6 contains three known domains: NTD (N-Terminal Domain), EXO (EXOribonuclease domain), and HRDC (Homology to RNase D domain C-terminal). It is hypothesized that a second HRDC domain (HRDC2) may be located C-terminal to HRDC. 3′ to 5′ distributive hydrolytic endoribonucleolytic activity is located within the EXO domain (green circle).