DcpS can act in the 5'-3' mRNA decay pathway in addition to the 3'-5' pathway.
Eukaryotic mRNA degradation proceeds through two main pathways, both involving mRNA cap breakdown. In the 3'-5' mRNA decay pathway, mRNA body degradation generates free m7GpppN that is hydrolyzed by DcpS generating m7GMP. In the 5'-3' pathway, the recently identified human Dcp2 decapping enzyme cleaves the cap of deadenylated mRNAs to produce m7GDP and 5'-phosphorylated mRNA. We investigated mRNA decay in human cell extracts by using a new assay for decapping. We observed that 5'-phosphorylated intermediates resulting from decapping appear after incubation of a substrate RNA in human cell extracts, indicating the presence of an active 5'-3' mRNA decay pathway. Surprisingly, however, the cognate m7GDP product was not detected, whereas abundant amounts of m7GMP were generated. Additional experiments revealed that m7GDP is, unexpectedly, efficiently converted to m7GMP in extracts from various organisms. The factor necessary and sufficient for this reaction was identified as DcpS in both yeast and human. m7GMP is thus a general, pathway-independent, by-product of eukaryotic mRNA decay. m7GDP breakdown should prevent misincorporation of methylated nucleotides in nucleic acids and could generate a unique indicator allowing the cell to monitor mRNA decay.
van Dijk
Erwin
E
Equipe Labellisée La Ligue, Centre de Génétique Moléculaire, Unité Propre de Recherche 2167, Centre National de la Recherche Scientifique Associée à l'Université Paris VI, Avenue de la Terrasse, 91198 Gif sur Yvette, France.
Le Hir
Hervé
H
Séraphin
Bertrand
B
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004722:Endoribonucleases / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008954:Models, Biological; D012315:RNA Caps / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D014981:Xenopus
D012315:RNA Caps; D012333:RNA, Messenger; D011994:Recombinant Proteins; C030052:mRNA decapping enzymes; C111106:7-methylguanosine 5'-diphosphate; D006153:Guanosine Diphosphate; D004722:Endoribonucleases; C467723:DCP2 protein, human