Nucleolar proteins regulate stage‐specific gene expression and ribosomal RNA maturation in T rypanosoma brucei

• Published in: Molecular microbiology 2013-05, Vol.88 (4), p.827-840
• Main Authors: Schumann Burkard, Gabriela, Käser, Sandro, de Araújo, Patrícia Rosa, Schimanski, Bernd, Naguleswaran, Arunasalam, Knüsel, Sebastian, Heller, Manfred, Roditi, Isabel
• Format: Article
• Language: English
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.12227

Different life‐cycle stages of T rypanosoma 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 ( N ucleolar R egulator of G PEET 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.