title: Unconventional rules of small nuclear RNA transcription and cap modification in trypanosomatids.
abstract: This review focuses on the spliced leader (SL) RNA and uridylic acid-rich small nuclear RNAs (U-snRNAs) involved in pre-mRNA processing in trypanosomatid protozoa, with particular emphasis on the mechanism of transcription and cap formation. The SL RNA plays a central role in mRNA biogenesis by providing the unique cap 4 structure to the 5' end of all mRNAs by trans-splicing. The trimethylguanosine capped U-snRNAs, on the other hand, represent an unusual example among eukaryotic snRNAs in that they are transcribed by RNA polymerase III. This implies the existence of a distinctive mechanism for capping enzyme selection by the transcriptional machinery. Furthermore, the transcription units of U-snRNA genes offer yet another example of the variety of choices that have been established during eukaryotic evolution, namely that an upstream tRNA gene or tRNA-like gene provides extragenic promoter elements for a downstream small RNA gene.
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520-8022, USA. christian.tschudi@yale.edu
authors.forename: Christian
authors.initials: C
authors.lastname: Tschudi
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Ullut
mesh_terms: D000818:Animals; D015226:Dinucleoside Phosphates / Q000378:metabolism; D019143:Evolution, Molecular; D005796:Genes; D005807:Genes, Overlapping; D008780:Methyltransferases / Q000378:metabolism; D011401:Promoter Regions, Genetic; D015800:Protozoan Proteins / Q000378:metabolism; D012315:RNA Caps / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012326:RNA Splicing; D016053:RNA, Protozoan / Q000235:genetics / Q000502:physiology*; D012342:RNA, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D020038:RNA, Spliced Leader / Q000235:genetics / Q000502:physiology*; D012343:RNA, Transfer / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism; D013045:Species Specificity; D017381:Spliceosomes / Q000378:metabolism; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics; D014351:Trypanosomatina / Q000235:genetics*
chemical_list: D015226:Dinucleoside Phosphates; D015800:Protozoan Proteins; D012315:RNA Caps; D012322:RNA Precursors; D016053:RNA, Protozoan; D012342:RNA, Small Nuclear; D020038:RNA, Spliced Leader; D017411:Ribonucleoproteins, Small Nuclear; C062229:7-methyl-diguanosine triphosphate; D012343:RNA, Transfer; C446079:16S rRNA - m7G methyltransferase; D008780:Methyltransferases; D012319:RNA Polymerase II