title: Identification of Drosophila and human 7-methyl GMP-specific nucleotidases.
abstract: Turnover of mRNA releases, in addition to the four regular nucleoside monophosphates, the methylated cap nucleotide in the form of 7-methylguanosine monophosphate (m(7)GMP) or diphosphate (m(7)GDP). The existence of pathways to eliminate the modified nucleotide seems likely, as its incorporation into nucleic acids is undesirable. Here we describe a novel 5' nucleotidase from Drosophila that cleaves m(7)GMP to 7-methylguanosine and inorganic phosphate. The enzyme, encoded by the predicted gene CG3362, also efficiently dephosphorylates CMP, although with lower apparent affinity; UMP and the purine nucleotides are poor substrates. The enzyme is inhibited by elevated concentrations of AMP and also cleaves m(7)GDP to the nucleoside and two inorganic phosphates, albeit less efficiently. CG3362 has equivalent sequence similarity to two human enzymes, cytosolic nucleotidase III (cNIII) and the previously uncharacterized cytosolic nucleotidase III-like (cNIII-like). We show that cNIII-like also displays 5' nucleotidase activity with a high affinity for m(7)GMP. CMP is a slightly better substrate but again with a higher K(m). The activity of cNIII-like is stimulated by phosphate. In contrast to cNIII-like, cNIII and human cytosolic nucleotidase II do not accept m(7)GMP as a substrate. We suggest that the m(7)G-specific nucleotidases protect cells against undesired salvage of m(7)GMP and its incorporation into nucleic acids.
authors.affiliation: Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, 06099 Halle, Germany.
authors.forename: Juliane
authors.initials: J
authors.lastname: Buschmann
authors.forename: Bodo
authors.initials: B
authors.lastname: Moritz
authors.forename: Mandy
authors.initials: M
authors.lastname: Jeske
authors.forename: Hauke
authors.initials: H
authors.lastname: Lilie
authors.forename: Angelika
authors.initials: A
authors.lastname: Schierhorn
authors.forename: Elmar
authors.initials: E
authors.lastname: Wahle
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003432:Cross-Linking Reagents / Q000737:chemistry; D006152:Cyclic GMP / Q000737:chemistry*; D004331:Drosophila melanogaster; D006801:Humans; D007700:Kinetics; D008239:Lysine / Q000737:chemistry; D008969:Molecular Sequence Data; D009708:Nucleotidases / Q000737:chemistry*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014466:Ultraviolet Rays; D014542:Uridine Monophosphate / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D012333:RNA, Messenger; D014542:Uridine Monophosphate; D009708:Nucleotidases; D006152:Cyclic GMP; D008239:Lysine