INCREASED EXPRESSION OF LD1 GENES TRANSCRIBED BY RNA-POLYMERASE-I IN LEISHMANIA-DONOVANI AS A RESULT OF DUPLICATION INTO THE RIBOSOMAL-RNA GENE LOCUS

Eukaryotic protein-coding genes are generally transcribed by RNA polym erase II (Pol II), which has a lower transcription rate than that of P ol I. We report here the duplication of two LD1 genes into the rRNA lo cus and their resultant transcription by Pol I. The multigenic LDI loc us is present in a 2.2-Mb chromosome in all stocks of Leishmania spp. and is also present in multicopy 200- to 450-kb linear chromosomes or multicopy circular DNAs in over 15% of stocks examined. Genomic rearra ngement in Leishmania donovani LSB-51.1 resulted in duplication of a 3 .9-kb segment of LDI containing two genes (orfF and orfG) and of a 1.3 -kb segment from similar to 10 kb downstream into the rRNA gene repeat region of the 1.2-Mb chromosome. Short sequences (12 or 13 bp) common to the 2.2-Mb LD1 and 1.2-Mb rRNA loci suggest that this gene convers ion occurred by homologous recombination. Transcription of the duplica ted genes is alpha-amanitin resistant, indicating transcription by pol I, in contrast to the a-amanitin-sensitive (Pol II) transcription of the genes in the 2.2-Mb LDI locus. This results in higher transcript a bundance than expected from the gene copy number in LSB-51.1 and in el evated expression of at least the orfF gene product.