Genes selectively expressed in the infectious (metacyclic) stage of Leishmania major promastigotes encode a potential basic-zipper structural motif.

Complementary DNA clones representing transcripts selectively expressed in the non-dividing, infective (metacyclic) stage of Leishmania major promastigotes (MP) were identified by differential and subtractive screening. The majority of the selected clones hybridized on Northern blots to a set of transcripts highly expressed by MP, but to a much lower extent in proliferating and stationary-phase attenuated promastigotes. Stationary, but not log-phase cultures, of each of 5 L. major strains showing a potential for differentiation to metacyclics, expressed these transcripts (MAT-1; MP-associated transcripts). From sequence analysis of full-length cDNA clones corresponding to the predominating MAT-1 species, an open reading frame encoding a 139 aa polypeptide (15.4 kDa) was predicted and supported by immunoprecipitation by kala-azar sera of reticulocyte extract translation products using in vitro transcribed RNA. Although no significant primary sequence homology to database nucleic acid and protein sequences was found, the sequence displays similarities to the basic-zipper families of transcription regulatory proteins.