Cloning and characterization of differentially expressed genes from in vitro-grown 'amastigotes' of Leishmania donovani.

Leishmanial parasites routinely undergo cyclic differentiation from promastigotes to amastigotes during their life cycle. This process involves both morphological and macromolecular changes. To study such changes, we used a axenic culture system which permits the continuous generation and cycling of Leishmania donovani from promastigotes to 'amastigotes' in vitro. cDNA libraries were constructed from poly(A)+ RNA isolated from both the pro- and amastigote forms. Using differential cDNA hybridization techniques, 3 unique cDNAs clones (P17, A41 and A45) were isolated from the amastigote library. To assess whether these clones were differentially expressed by the pro-or 'amastigotes' forms, they were hybridized to RNA isolated from each of these parasite forms in Northern and slot-blots. Results of these analyses showed that 'amastigotes' had approx. 2-fold higher levels of the A41 and A45 RNAs compared to the promastigotes. Conversely, promastigotes showed approx. 2-fold higher levels of the P17 RNA than 'amastigotes'. Nucleotide sequence analysis and comparison with those in Gene bank, revealed that the 3 cDNAs represent unique leishmanial genes. Comparison of the deduced amino acid sequences revealed that P17 open reading frame (ORF) had significant similarity with a soybean ribosomal protein S11; A41 ORF with a Bacillus subtilis spore germination gene (gerC) and A45 ORF with yeast stress-inducible protein (STI1). It is of interest to note that, of the 3 cDNAs identified, the A45-encoded protein was recognized by sera from patients with clinically active visceral leishmaniasis and was encoded by a single copy gene.