Transcription of Leishmania major Friedlin chromosome 1 initiates in both directions within a single region

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 similar to10-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 11 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.