title: Nematode m7GpppG and m3(2,2,7)GpppG decapping: activities in Ascaris embryos and characterization of C. elegans scavenger DcpS.
abstract: A spliced leader contributes the mature 5'ends of many mRNAs in trans-splicing organisms. Trans-spliced metazoan mRNAs acquire an m3(2,2,7)GpppN cap from the added spliced leader exon. The presence of these caps, along with the typical m7GpppN cap on non-trans-spliced mRNAs, requires that cellular mRNA cap-binding proteins and mRNA metabolism deal with different cap structures. We have developed and used an in vitro system to examine mRNA degradation and decapping activities in nematode embryo extracts. The predominant pathway of mRNA decay is a 3' to 5' pathway with exoribonuclease degradation of the RNA followed by hydrolysis of resulting mRNA cap by a scavenger (DcpS-like) decapping activity. Direct decapping of mRNA by a Dcp1/Dcp2-like activity does occur, but is approximately 15-fold less active than the 3' to 5' pathway. The DcpS-like activity in nematode embryo extracts hydrolyzes both m7GpppG and m3(2,2,7)GpppG dinucleoside triphosphates. The Dcp1/Dcp2-like activity in extracts also hydrolyzes these two cap structures at the 5' ends of RNAs. Interestingly, recombinant nematode DcpS differs from its human ortholog in its substrate length requirement and in its capacity to hydrolyze m3(2,2,7)GpppG.
authors.affiliation: Department of Biology, City univiersity of new york, Graduate Center, Staten Island, 10314, USA.
authors.forename: Leah S
authors.initials: LS
authors.lastname: Cohen
authors.forename: Claudette
authors.initials: C
authors.lastname: Mikhli
authors.forename: Cassandra
authors.initials: C
authors.lastname: Friedman
authors.forename: Marzena
authors.initials: M
authors.lastname: Jankowska-Anyszka
authors.forename: Janusz
authors.initials: J
authors.lastname: Stepinski
authors.forename: Edward
authors.initials: E
authors.lastname: Darzynkiewicz
authors.forename: Richard E
authors.initials: RE
authors.lastname: Davis
mesh_terms: D000818:Animals; D001200:Ascaris / Q000196:embryology / Q000378:metabolism*; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism; D015226:Dinucleoside Phosphates / Q000378:metabolism*; D004722:Endoribonucleases / Q000378:metabolism; D006868:Hydrolysis; D012315:RNA Caps / Q000378:metabolism*; D018510:RNA, Helminth / Q000378:metabolism*; D020038:RNA, Spliced Leader / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D029742:Caenorhabditis elegans Proteins; D015226:Dinucleoside Phosphates; D012315:RNA Caps; D018510:RNA, Helminth; D020038:RNA, Spliced Leader; D011994:Recombinant Proteins; C030052:mRNA decapping enzymes; C062229:7-methyl-diguanosine triphosphate; D004722:Endoribonucleases