REGULATION AND TRAFFICKING OF 3 DISTINCT 18-S RIBOSOMAL-RNAS DURING DEVELOPMENT OF THE MALARIA PARASITE

The human malaria parasite Plasmodium vivax has been shown to regulate the transcription of two distinct 18 RNAs during development. Here we show a third and distinctive type of ribosome that is present shortly after zygote formation, a transcriptional pattern of ribosome types t hat relates closely to the developmental state of the parasite and a p henomenon that separates ribosomal types at a critical phase of matura tion. The A-type ribosome is predominantly found in infected erythrocy tes of the vertebrate and the mosquito blood meal. Transcripts from th e A gene are replaced by transcripts from another locus, the O gene, s hortly after fertilization and increase in number as the parasite deve lops on the mosquito midgut. Transcripts from another locus, the S gen e, begins as the oocyst form of the parasite matures. RNA transcripts from the S gene are preferentially included in sporozoites that bud of f from the oocyst and migrate to the salivary gland while the O gene t ranscripts are left within the oocyst. Although all three genes are ty pically eukaryotic in structure, the O gene transcript, described here , varies from the other two in core regions of the rRNA that are invol ved in mRNA decoding and translational termination. We now can correla te developmental progression of the parasite with changes in regions o f rRNA sequence that are broadly conserved, where sequence alterations have been related to function in other systems and whose effects can be studied outside of Plasm odium. This should allow assessment of the role of translational control in parasite development. (C) 1997 Acade mic Press Limited.