Genomic organization and expression of two independent gene arrays coding for two antigenic acidic ribosomal proteins of Leishmania.

In the present paper we describe the isolation and characterization of four novel genes of the parasitic protozoan Leishmania infantum. These genes are organized as two independent gene clusters, and they are related by nucleotide sequence to eukaryotic genes encoding acidic ribosomal proteins. Each gene cluster contains two tandemly linked genes coding for identical proteins. Each of the proteins coded by the gene clusters (called LiP and LiP') are highly divergent in sequence, showing the characteristic features of eukaryotic P-proteins from the P2 group. In spite of the sequence conservation of the coding regions of each of the genes in the cluster, the 5'- and 3'-untranslated regions are heterogeneous in sequence. The analysis of the expression of these genes indicates that logarithmic phase promastigotes show increased levels of LiP- and LiP'-specific transcripts compared with stationary phase promastigotes. The steady state RNA levels of the LiP and LiP' genes show a similar dependence of the growth phase of the parasite. Using specific probes for the divergent 3'-untranslated regions of each of the genes, it was found that the abundance of the mature transcripts is different even when the transcripts are derived from the same gene cluster. These findings probably indicate that the 3'-untranslated regions may influence the stability or turnover of the transcripts derived from both LiP and LiP' gene clusters.