A 140-bp AT-rich sequence mediates positive and negative transcriptional control of a Plasmodium falciparum developmentally regulated promoter.

摘要

Little is known about the structure of malaria parasite gene promoters and how their activity is regulated during parasite development. We here report results of a functional study of the genomic flanking regions of the Plasmodium falciparum gametocyte-specific gene pfg27, whose promoter is inactive in asexual parasites and is specifically switched on at the onset of gametocytogenesis. Promoter deletion analysis with plasmids containing the green fluorescent protein reporter, conducted on asexual and sexual stage parasites of clone 3D7, showed that 140bp immediately preceding the pfg27 transcription start sites are sufficient to achieve timing and specificity of gene expression comparable to those of the endogenous pfg27 gene. Observations that the promoter sequences were functioning on episomal plasmids, and our failure to detect dramatic alterations in DNaseI hypersensitivity in the pfg27 chromosomal upstream region upon activation of the endogenous promoter, suggest that chromatin conformation may not have a major influence on the developmental regulation of the pfg27 promoter. Further deletion analysis of the 140bp promoter led to identification of sequences involved in the repression of the pfg27 promoter in a sub-population of asexual parasites, and of sequences required for the efficient gametocyte-specific transcription of the gene, the latter characterised by the presence of long homopolymeric dA and dT tracts. These results together indicate that in P. falciparum short sequences of apparent minimal complexity nevertheless contain sufficient genetic information to act as a promoter responsive to developmental regulation. In this analysis, the functional role of the downstream flanking region of pfg27 was also investigated, revealing that the gene 3' untranslated region contributes to stability of the pfg27 transcript in the maturation of P. falciparum gametocytes.