Trypanosome spliced leader RNA genes contain the first identified RNA polymerase II gene promoter in these organisms

Abstract

Typical general transcription factors, such as TATA binding protein and TFII B, have not yet been identified in any member of the Trypanosomatidae family of parasitic protozoa. Interestingly, mRNA coding genes do not appear to have discrete transcriptional start sites, although in most cases they require an RNA polymerase that has the biochemical properties of eukaryotic RNA polymerase II. A discrete transcription initiation site may not be necessary for mRNA synthesis since the sequences upstream of each transcribed coding region are trimmed from the nascent transcript when a short m(7)G-capped RNA is added during mRNA maturation. This short 39 nt m(7)G-capped RNA, the spliced leader (SL) sequence, is expressed as an approximately 100 nt long RNA from a set of reiterated, though independently transcribed, genes in the trypanosome genome. Punctuation of the 5' end of mRNAs by a m(7)G cap-containing spliced leader is a developing theme in the lower eukaryotic world; organisms as diverse as EUGLENA: and nematode worms, including Caenorhabditis elegans, utilize SL RNA in their mRNA maturation programs. Towards understanding the coordination of SL RNA and mRNA expression in trypanosomes, we have begun by characterizing SL RNA gene expression in the model trypanosome Leptomonas seymouri. Using a homologous in vitro transcription system, we demonstrate in this study that the SL RNA is transcribed by RNA polymerase II. During SL RNA transcription, accurate initiation is determined by an initiator element with a loose consensus of CYAC/AYR(+1). This element, as well as two additional basal promoter elements, is divergent in sequence from the basal transcription elements seen in other eukaryotic gene promoters. We show here that the in vitro transcription extract contains a binding activity that is specific for the initiator element and thus may participate in recruiting RNA polymerase II to the SL RNA gene promoter.

Identification of novel snRNA-specific Sm proteins that bind selectively to U2 and U4 snRNAs in Trypanosoma brucei

“…The U snRNAs are transcribed in trypanosomes by RNA polymerase III from extragenic tRNA promoters (Nakaar et al 1994). In contrast, the SL RNA is transcribed by an RNA polymerase II-dependent extragenic promoter (Gilinger and Bellofatto 2001;Das et al 2005). Strong evidence was provided for coupling of the unique hypermethylated capping of SL RNA and its transcription (Mair et al 2000).…”

TcUBP-1, an mRNA Destabilizing Factor from Trypanosomes, Homodimerizes and Interacts with Novel AU-rich Element- and Poly(A)-binding Proteins Forming a Ribonucleoprotein Complex

“…RNA polymerase I promoters were identified in rDNA but also in genes encoding the variable surface antigens from African trypanosomes (1). Conversely, only few RNA polymerase II promoters were described (2). As part of the maturation process, a common 39-nucleotide RNA, named spliced leader, is added to all trypanosome mRNAs by a trans-splicing process.…”

TcUBP-1, a Developmentally Regulated U-rich RNA-binding Protein Involved in Selective mRNA Destabilization in Trypanosomes

“…Two putative promoter regions were described as transcriptionally void regions upstream from the highly transcribed actin and Hsp70 genes (22,23). However, one example of RNA polymerase II promoter was recently identified in the spliced leader genes of the parasite Leptomonas seymouri (24). Thus, trypanosomes are interesting organisms in the analysis of post-transcriptional regulatory mechanisms affecting mRNA expression patterns (25).…”