Overlapping sense and antisense transcription units in Trypanosoma brucei.
Procyclins are the major surface glycoproteins of insect-form Trypanosoma brucei. The procyclin expression sites are polycistronic and are transcribed by an alpha-amanitin-resistant polymerase, probably RNA polymerase I (Pol I). The expression sites are flanked by transcription units that are sensitive to alpha-amanitin, which is a hallmark of Pol II-driven transcription. We have analysed a region of 9.5 kb connecting the EP/PAG2 expression site with the downstream transcription unit. The procyclin expression site is longer than was previously realized and contains an additional gene, procyclin-associated gene 4 (PAG4), and a region of unknown function, the T region, that gives rise to trans-spliced, polyadenylated RNAs containing small open reading frames (ORFs). Two new genes, GU1 and GU2, were identified in the downstream transcription unit on the opposite strand. Unexpectedly, the 3' untranslated region of GU2 and the complementary T transcripts overlap by several hundred base pairs. Replacement of GU2 by a unique tag confirmed that sense and antisense transcription occurred from a single chromosomal locus. Overlapping transcription is stage specific and may extend > or = 10 kb in insect-form trypanosomes. The nucleotide composition of the T. brucei genome is such that antisense ORFs occur frequently. If stable mRNAs can be derived from both strands, the coding potential of the genome may be substantially larger than has previously been suspected.
Liniger
M
M
Institut für Zellbiologie, Universität Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland.
Bodenmüller
K
K
Pays
E
E
Gallati
S
S
Roditi
I
I
D020413:3' Untranslated Regions; D000818:Animals; D016373:DNA, Antisense / Q000235:genetics*; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000235:genetics; D008869:Microtubule-Associated Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D015800:Protozoan Proteins / Q000235:genetics*; D012318:RNA Polymerase I / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics*
D020413:3' Untranslated Regions; D016373:DNA, Antisense; C432138:GU1 protein, Trypanosoma brucei; C432139:GU2 protein, Trypanosoma brucei; D006023:Glycoproteins; C073903:MARP-1 protein, Trypanosoma brucei; D008869:Microtubule-Associated Proteins; C432137:PAG4 protein, Trypanosoma brucei; D015800:Protozoan Proteins; C078011:ESAG 7 protein, Trypanosoma brucei; D012318:RNA Polymerase I