title: Roles of a Trypanosoma brucei 5'->3' exoribonuclease homolog in mRNA degradation.
abstract: The genome of the kinetoplastid parasite Trypanosoma brucei encodes four homologs of the Saccharomyces cerevisiae 5'-->3' exoribonucleases Xrn1p and Xrn2p/Rat1p, XRNA, XRNB, XRNC, and XRND. In S. cerevisiae, Xrn1p is a cytosolic enzyme involved in degradation of mRNA, whereas Xrn2p is involved in RNA processing in the nucleus. Trypanosome XRND was found in the nucleus, XRNB and XRNC were found in the cytoplasm, and XRNA appeared to be in both compartments. XRND and XRNA were essential for parasite growth. Depletion of XRNA increased the abundances of highly unstable developmentally regulated mRNAs, perhaps by delaying a deadenylation-independent decay pathway. Degradation of more stable or unregulated mRNAs was not affected by XRNA depletion although a slight decrease in average poly(A) tail length was observed. We conclude that in trypanosomes 5'-->3' exonuclease activity is important in degradation of highly unstable, regulated mRNAs, but that for other mRNAs another step is more important in determining the decay rate.
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg (ZMBH), D-69120 Heidelberg, Germany.
authors.forename: Chi-Ho
authors.initials: CH
authors.lastname: Li
authors.forename: Henriette
authors.initials: H
authors.lastname: Irmer
authors.forename: Drifa
authors.initials: D
authors.lastname: Gudjonsdottir-Planck
authors.forename: Simone
authors.initials: S
authors.lastname: Freese
authors.forename: Heike
authors.initials: H
authors.lastname: Salm
authors.forename: Simon
authors.initials: S
authors.lastname: Haile
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Estévez
authors.forename: Christine
authors.initials: C
authors.lastname: Clayton
mesh_terms: D020413:3' Untranslated Regions / Q000378:metabolism; D000199:Actins / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000201:enzymology; D005095:Exoribonucleases / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D016830:Kinetoplastida / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family; D011061:Poly A; D020871:RNA Stability; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions; D014346:Trypanosoma brucei brucei / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development
chemical_list: D020413:3' Untranslated Regions; D000199:Actins; D029701:Saccharomyces cerevisiae Proteins; C075577:RAT1 protein, S cerevisiae; D011061:Poly A; D005095:Exoribonucleases