Transcription of Leishmania major Friedlin Chromosome 1 Initiates in Both Directions within a Single Region

Abstract

Almost nothing is known about the sequences involved in transcription initiation of protein-coding genes in the parasite Leishmania. We describe here the transcriptional analysis of chromosome 1 (chr1) from Leishmania major Friedlin (LmjF) which encodes the first 29 genes on one DNA strand, and the remaining 50 on the opposite strand. Strand-specific nuclear run-on assays showed that a low level of nonspecific transcription probably takes place over the entire chromosome, but an approximately 10-fold higher level of coding strand-specific RNA polymerase II (Pol II)-mediated transcription initiates within the strand-switch region. 5' RACE studies localized the initiation sites to a <100 bp region. Transfection studies support the presence of a bidirectional promoter within the strand-switch region, but suggest that other factors are also involved in Pol II transcription. Thus, while in most eukaryotes each gene possesses its own promoter, a single region seems to drive the expression of the entire chr1 in LmjF.

Analysis of the Leishmania donovani transcriptome reveals an ordered progression of transient and permanent changes in gene expression during differentiation

“…Unlike in most other eukaryotes, the protein-coding genes in Leishmania (and other trypanosomatids) are organized into large polycistronic gene clusters (PGCs) with tens-to-hundreds of adjacent genes [25,29] apparently transcribed from a single RNA polymerase II transcription initiation site [27,28]. Only eight of the 125 PGCs examined showed evidence for correlation of gene expression profiles that was significantly different (p<0.01) from that expected by chance (Table IV).…”

“…Regulation of gene expression in Leishmania is unusual because their protein-coding genes are transcribed as polycistronic RNAs with tens-to-hundreds of adjacent genes on the same DNA strand [25][26][27][28][29]. Mature mRNAs are subsequently obtained from coordinated polyadenylation and trans-splicing, which adds a 39-nt spliced leader (SL) sequence to the 5' end of all mRNAs [30,31].…”

Characterization of the RNA polymerase II and III complexes in Leishmania major

“…Leishmania and other trypanosomatids possess unique mechanisms of gene expression (Clayton, 2002;Campbell et al, 2003). Transcription in these organisms initiates at only a few regions on each chromosome (Martinez-Calvillo et al, 2003, 2004) and mature nuclear mRNAs are generated from the polycistronic transcripts by trans-splicing, a process that adjoins a 39-nucleotide capped spliced-leader (SL) to the 5′ end of all the mRNAs (Parsons et al, 1984). Post-transcriptional mechanisms appear to regulate the steady-state levels of most of the mRNAs (Clayton, 2002).…”

Regulatory elements involved in the post-transcriptional control of stage-specific gene expression in Trypanosoma cruzi: a review

“…Transcription is initiated bi-directionally between two divergent gene clusters (Martínez-Calvillo et al 2003 to produce polycistronic premRNAs that are subsequently processed (Figure). With the exception of the spliced leader (SL) promoter, no promoter that is recognised by RNA polymerase II has been identified, and only a few transcription factors have been described (Cribb & Serra 2009, Cribb et al 2010.…”