Molecular Characterization of 5S Ribosomal RNA Genes and Transcripts in the Protozoan Parasiteleishmania Major

SUMMARYEukaryotic 5S rRNA, synthesized by RNA polymerase III (Pol III), is an essential component of the large ribosomal subunit. Most organisms contain hundreds of 5S rRNA genes organized into tandem arrays. However, the genome of the protozoan parasiteLeishmania majorcontains only 11 copies of the 5S rRNA gene, which are interspersed and associated with other Pol III-transcribed genes. Here we report that, in general, the number and order of the 5S rRNA genes is conserved between different species ofLeishmania. While in most organisms 5S rRNA genes are normally associated with the nucleolus, combined fluorescentin situhybridization and indirect immunofluorescence experiments showed that 5S rRNA genes are mainly located at the nuclear periphery inL. major. Similarly, the tandemly repeated 5S rRNA genes inTrypanosoma cruziare dispersed throughout the nucleus. In contrast, 5S rRNA transcripts inL. majorwere localized within the nucleolus, and scattered throughout the cytoplasm, where mature ribosomes are located. Unlike other rRNA species, stable antisense RNA complementary to 5S rRNA is not detected inL. major.