TY - JOUR
T1 - The human homolog of Escherichia coli Orn degrades small single-stranded RNA and DNA oligomers
AU - Nguyen, Lam H.
AU - Erzberger, Jan P.
AU - Root, Jeffrey
AU - Wilson, David M.
PY - 2000/8/25
Y1 - 2000/8/25
N2 - We report here the identification of human homologues to the essential Escherichia coli Orn protein and the related yeast mitochondrial DNA-escape pathway regulatory factor Ynt20. The human proteins appear to arise from alternatively spliced transcripts, and are thus identical, except the human Ynt20 equivalent contains an NH2-terminal extension that possesses a predicted mitochondrial protease cleavage signal. In vitro analysis revealed that the smaller human protein exhibits a 3' to 5' exonuclease activity for small (primarily ≤5 nucleotides in length) single-stranded RNA and DNA oligomers. We have named this human protein Sfn for small fragment nuclease to reflect its broad substrate range, and have termed the longer protein hSfnα. Sfn prefers Mn2+ as a metal cofactor and displays a temperature-resistant (to 50 °C) nuclease activity. Kinetic analysis indicates that Sfn exhibits a similar affinity for small RNAs and DNAs (K(m) of ~1.5 μM), but degrades small RNAs ~4-fold more efficiently than DNA. Mutation of a conserved aspartate (Asp136) to alanine abolishes both nuclease activities of Sfn. Northern blot analysis revealed that a 1-kilobase transcript corresponding to SFN and/or SFNα (these mRNAs differ by only two nucleotides) is expressed at varying levels in all fetal and adult human tissues examined. Expressed tag sequence clone analysis found that the two splice variants, SFN to SFNα, are present at a ratio of roughly 4 to 1, respectively. The results presented within suggest a role for human Sfn in cellular nucleotide recycling.
AB - We report here the identification of human homologues to the essential Escherichia coli Orn protein and the related yeast mitochondrial DNA-escape pathway regulatory factor Ynt20. The human proteins appear to arise from alternatively spliced transcripts, and are thus identical, except the human Ynt20 equivalent contains an NH2-terminal extension that possesses a predicted mitochondrial protease cleavage signal. In vitro analysis revealed that the smaller human protein exhibits a 3' to 5' exonuclease activity for small (primarily ≤5 nucleotides in length) single-stranded RNA and DNA oligomers. We have named this human protein Sfn for small fragment nuclease to reflect its broad substrate range, and have termed the longer protein hSfnα. Sfn prefers Mn2+ as a metal cofactor and displays a temperature-resistant (to 50 °C) nuclease activity. Kinetic analysis indicates that Sfn exhibits a similar affinity for small RNAs and DNAs (K(m) of ~1.5 μM), but degrades small RNAs ~4-fold more efficiently than DNA. Mutation of a conserved aspartate (Asp136) to alanine abolishes both nuclease activities of Sfn. Northern blot analysis revealed that a 1-kilobase transcript corresponding to SFN and/or SFNα (these mRNAs differ by only two nucleotides) is expressed at varying levels in all fetal and adult human tissues examined. Expressed tag sequence clone analysis found that the two splice variants, SFN to SFNα, are present at a ratio of roughly 4 to 1, respectively. The results presented within suggest a role for human Sfn in cellular nucleotide recycling.
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U2 - 10.1074/jbc.M002672200
DO - 10.1074/jbc.M002672200
M3 - Article
C2 - 10851236
AN - SCOPUS:0034714196
SN - 0021-9258
VL - 275
SP - 25900
EP - 25906
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 34
ER -