Trypanosomes transcription

Trans splicing. Every mRNA in trypanosomes has, at its 5 end, a short 35-nucleotide sequence that is not encoded in the transcribed gene. It was found that for each mRNA molecule two transcripts are formed and are spliced together, always with the 5 piece from a short SL (spliced leader) gene being joined to each of the others.639 This trans splicing has since been observed in many plants, animals, and protists.640... 

Polycistronic transcription units are typical of prokaryotic organisms and of some eukaryotic viruses. Trypanosomes (and nematodes which also trans-splice, see below) represent the only examples of eukaryotes which transcribe their genes in this way. At present, there is no evidence that the various genes encoded in polycistronic transcription units in trypanosomes are related in their function as are operons in bacteria. Likewise, we do not know what the average size of a transcription unit is in trypanosomatids and whether there is any attenuation of transcription in regions that are promoter-distal relative to those that are promoter-proximal. This latter consideration has obvious relevance for the control of gene expression in these organisms. 

As discussed above, trans-splicing serves to mature 5 ends of mRNAs embedded with polycistronic transcription units in trypanosomes and may serve the same function in nematodes. However, trans-splicing may be important in other aspects of mRNA metabolism. 

Muhich, M. L. and Boothroyd, J. C. (1988) Polycistronic transcripts in trypanosomes and their accumulation during heat shock evidence for a precursor role in mRNA synthesis. Mol. Cell Biol. 8 3837-3846. 

Tschudi, C. and Ullu, E. (1988) Polygene transcripts are precursors to calmodulin mRNAs in trypanosomes. EMBO J. 7 455-463. 

Ullu, E., Matthews, K. R. and Tschudi, C. (1993) Temporal order of RNA process reactions in trypanosomes rapid trans-splicing precedes polyadenylation of newly-synthesized tubulin transcripts. Mol. Cell Biol. 13 720 725. 

Borst, P. (1986) Discontinuous transcription and antigenic variation in trypanosomes. Annu. Rev. Biochem. 55 701-732. 

Grams J> Morris JC, Drew ME et al. A trypanosome mitochondrial RNA polymerase is required for transcription and replication. J Biol Chiem 2002 277(19) 16952-9. 

Van der Ploeg LH. Discontinuous transcription and splicing in trypanosomes. Cell 1986 ... 

Perry K, A bian N. mRNA processing in the Ttypanosomatidae. Experientia 1991 47 118-128. Das A, Zhang Q, Palenchar JB et al. Trypanosomal TBP functions with the multisubunit transcription factor tSNAP to direct spliced-leader RNA gene expression. Mol Cell Biol 2005 ... 

Palenchar JB, Liu W, Palenchar PM et al. A divergent transcription factor TFIIB in trypanosomes is required for RNA polymerase Il-dependent SL RNA transcription and cell viability. Eukaryot Cell 2006 5(2) 293-300. 

The various forms of electron microscopy (EM) have been used to examine structural features of nucleic acid-protein interactions. EM structures include protein interactions with the ribosome, an activator-dependent transcription initiation complex, the core editing complex in trypanosomatid mitochondria, human Dicer from the RISC complex showing that it has an L-shaped structure, the RNA editing complex from trypanosomes and loading of minichromosome maintenance proteins (Mcm2-7) onto DNA during DNA replication. Scanning electrochemical microscopy (SECM) with DNA attached to an electrode has been used to detect an A-C mismatch site, and to visualise the activity of an enzyme to detect hybridisation. " Cryo-EM (CEM) has also been... 

Palenchar JB, Bellofatto V. Gene transcription in trypanosomes. Mol Bioehem Parasitol. 2006 145 135 1. 

---