Transcription initiation and termination on Leishmania major chromosome 3.

Genome projects involving Leishmania and other trypanosomatids have revealed that most genes in these organisms are organized into large clusters of genes on the same DNA strand. We have previously shown that transcription of the entire Leishmania major Friedlin (LmjF) chromosome 1 (chr1) initiates bidirectionally between two divergent gene clusters. Here, we analyze transcription of LmjF chr3, which contains two convergent clusters of 67 and 30 genes, separated by a tRNA gene, with a single divergent protein-coding gene located close to the "left" telomere. Nuclear run-on analyses indicate that specific transcription of chr3 initiates bidirectionally between the single subtelomeric gene and the adjacent 67-gene cluster, close to the "right" telomere upstream of the 30-gene cluster, and upstream of the tRNA gene. Transcription on both strands terminates within the tRNA-gene region. Transient-transfection studies support the role of the tRNA-gene region as a transcription terminator for RNA polymerase II (Pol II) and Pol III, and also for Pol I.