Transcription of the intergenic regions of the tubulin gene cluster ofTrypanosoma brucei: evidence for a polyclstronic transcription unit in a eukaryote

Abstract

The tubulin genes of T. brucei are clustered in a tightly packed array of alternating alpha- and beta-genes. The steady state mRNA contains one abundant mRNA species each for alpha- and beta-tubulin, both carrying the identical 35 nt mini-exon sequence at their 5'-ends. We have used in vitro run-on transcription assays to investigate the mechanism of tubulin gene transcription in T. brucei. Our results show that the regions between the individual tubulin genes are transcribed at the same rate as are the genes themselves. On the other hand, transcripts containing the intergenic regions could not be detected by Northern analysis or in vivo labelling experiments. We conclude that putative transcripts from the intergenic regions have a half-life of less than one minute. These results suggest that the tubulin gene cluster is transcribed as a single contiguous transcription unit yielding a primary transcript which is rapidly processed into individual mRNAs by the polyadenylation and mini-exon trans splicing machineries.

α‐ and β‐tubulin mRNAs of Trypanosoma cruzi originate from a single multicistronic transcript

“…In T. brucei and L. seymouri [12,16] the occurrence of primary transcripts from multicistronic DNA units has been shown by analysis of nascent transcripts. However, in many cases it was not possible to identify clearly the precursors in the steady-state RNA population [14,16]. In T. cruzi evidence for stable multicistronic precursors has been presented, initially for the IF-8 multigenic unit [17], and now also for the tubulin gene cluster.…”

“…The difficulty in detecting multicistronic precursors in steady-state RNAs indicates rapid processing of the primary transcript as described for T. brucei [14] and L. seymouri [161. In T. cruzi, in contrast, the multicistronic transcripts described, i.e.…”

“…It was shown that the mRNAs for the cytochrome-c oxidase subunit II and III contain uridine residues that are not encoded by the respective genes [I0, I 1]. Another unique feature of the RNA metabolism of trypanosomatids is the occurrence of multicistronic transcripts comprising different mRNA units: variant surface glycoprotein 221-a mRNA and seven other stable mRNAs [12,13]; c~-and fltubulins mRNAs [14]; phosphoglycerate kinase mRNAs [15], all in T. brucei; cr-tubulin mRNA in Leptomonas seymouri [16] and the IF-8 multigenic unit in T. cruzi [17]. In the majority of the cases the multicistronic RNA precursor was not clearly detected in Northern blots; one exception is the RNA from the IF-8 unit in T. cruzi.…”

Comparative interactomics provides evidence for functional specialization of the nuclear pore complex

“…Examples include antigenic variation, GPI-anchored proteins, RNA editing, polycistronic transcription and trans-splicing. [63][64][65][66][67] Originally considered a "quirky" character of these parasites, these fundamental biologic processes have now been found to be common in other eukaryotes (including RNA editing in mammals, 68,69 polycistronic transcription and trans-splicing in the nematode Caenorhabditis elegans). 70,71 Now, the trypanosome is performing this function again, providing insights into the structure and evolution of the NPC and mechanisms of nucleocytoplasmic transport.…”

Dinoflagellate tandem array gene transcripts are highly conserved and not polycistronic

“…This observation, in concert with the discovery of transsplicing in dinoflagellates, has led to the proposal that dinoflagellate transcripts are polycistronic (11). This proposal is largely derived from studies in kinetoplastids, in which transsplicing and polyadenylation are used to excise ORFs from polycistronic transcripts (12). Although attractive, this proposal has not yet been tested experimentally in dinoflagellates.…”