title: Nucleolar proteins regulate stage-specific gene expression and ribosomal RNA maturation in Trypanosoma brucei.
abstract: Different life-cycle stages of Trypanosoma brucei are characterized by stage-specific glycoprotein coats. GPEET procyclin, the major surface protein of early procyclic (insect midgut) forms, is transcribed in the nucleolus by RNA polymerase I as part of a polycistronic precursor that is processed to monocistronic mRNAs. In culture, when differentiation to late procyclic forms is triggered by removal of glycerol, the precursor is still transcribed, but accumulation of GPEET mRNA is prevented by a glycerol-responsive element in the 3' UTR. A genome-wide RNAi screen for persistent expression of GPEET in glycerol-free medium identified a novel protein, NRG1 (Nucleolar Regulator of GPEET 1), as a negative regulator. NRG1 associates with GPEET mRNA and with several nucleolar proteins. These include two PUF proteins, TbPUF7 and TbPUF10, and BOP1, a protein required for rRNA processing in other organisms. RNAi against each of these components prolonged or even increased GPEET expression in the absence of glycerol as well as causing a significant reduction in 5.8S rRNA and its immediate precursor. These results indicate that components of a complex used for rRNA maturation can have an additional role in regulating mRNAs that originate in the nucleolus.
authors.affiliation: Institute of Cell Biology, University of Bern, Bern, Switzerland.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Schumann Burkard
authors.forename: Sandro
authors.initials: S
authors.lastname: Käser
authors.forename: Patrícia Rosa
authors.initials: PR
authors.lastname: de Araújo
authors.forename: Bernd
authors.initials: B
authors.lastname: Schimanski
authors.forename: Arunasalam
authors.initials: A
authors.lastname: Naguleswaran
authors.forename: Sebastian
authors.initials: S
authors.lastname: Knüsel
authors.forename: Manfred
authors.initials: M
authors.lastname: Heller
authors.forename: Isabel
authors.initials: I
authors.lastname: Roditi
mesh_terms: D005786:Gene Expression Regulation; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D015800:Protozoan Proteins / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012335:RNA, Ribosomal / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism
chemical_list: C406751:GPEET protein, Trypanosoma brucei; D008562:Membrane Glycoproteins; D009687:Nuclear Proteins; D015800:Protozoan Proteins; D012335:RNA, Ribosomal; D016601:RNA-Binding Proteins