title: RNase 8, a novel RNase A superfamily ribonuclease expressed uniquely in placenta.
abstract: We report the identification and characterization of the gene encoding the eighth and final human ribonuclease (RNase) of the highly diversified RNase A superfamily. The RNase 8 gene is linked to seven other RNase A superfamily genes on chromosome 14. It is expressed prominently in the placenta, but is not detected in any other tissues examined. Phylogenetic analysis suggests that RNase 7 is the closest relative of RNase 8 and that the pair likely resulted from a recent gene duplication event in primates. Further analysis reveals that the RNase 8 gene has incorporated non-silent mutations at an elevated rate (1.3 x 10(-9) substitutions/site/year) and that orthologous RNase 8 genes from 6 of 10 primate species examined have been deactivated by frameshifting deletions or point mutations at crucial structural or catalytic residues. The ribonucleolytic activity of recombinant human RNase 8 is among the lowest of members of this superfamily and it exhibits neither antiviral nor antibacterial activities characteristic of some other RNase A ribonucleases. The rapid evolution, species-limited deactivation and tissue-specific expression of RNase 8 suggest a unique physiological function and reiterates the evolutionary plasticity of the RNase A superfamily.
authors.affiliation: Laboratory of Host Defenses, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA. jianzhi@umich.edu
authors.forename: Jianzhi
authors.initials: J
authors.lastname: Zhang
authors.forename: Kimberly D
authors.initials: KD
authors.lastname: Dyer
authors.forename: Helene F
authors.initials: HF
authors.lastname: Rosenberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D006801:Humans; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010802:Phylogeny; D010920:Placenta / Q000201:enzymology*; D011257:Pregnancy Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000502:physiology; D011323:Primates; D012333:RNA, Messenger / Q000096:biosynthesis; D012260:Ribonucleases / Q000096:biosynthesis* / Q000235:genetics* / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014018:Tissue Distribution
chemical_list: D011257:Pregnancy Proteins; D012333:RNA, Messenger; D012260:Ribonucleases; C448983:RNASE8 protein, human