Plasmodium falciparum: hrp3 promoter region is associated with stage-specificity and episomal recombination.

The asexual blood stage of Plasmodium falciparum in the human host is comprised of morphologically distinct ring, trophozoite and schizont stages, each of which possesses a distinct pattern of gene expression. Episomal promoter recombination has been recently reported in malaria parasites. We aim to investigate the nature of this process, and its relationship with promoter activity by employing a series of nested deletions of the ring-specific hrp3 promoter. Our results showed a discrete promoter region that is preferentially used for recombination. The P. falciparum hrp3 mRNA is only seen in ring-stage parasites but deletion of the recombination region was associated with decreased ring-stage expression and concurrent detection of transcripts in trophozoite-stage parasites. Our results describe a ring-stage specific regulatory region possibly involved in episomal promoter recombination, suggesting that common sequences might mediate both processes.