ANALYSIS OF MALARIAL TRANSCRIPTS USING CDNA-DIRECTED POLYMERASE CHAIN-REACTION

A polymerase chain reaction (PCR)-based approach is being employed to study RNA transcripts in malarial parasites, a system that is not easi ly amenable to molecular studies. Our aim is to compare messages from different life cycle stages to determine whether regulatory informatio n is encoded in the structure of plasmodial transcripts as a result of differential RNA processing. In particular, we have analyzed the stru cture of the message encoding the circumsporozoite (CS) protein of the murine malaria Plasmodium berghei, the immunodominant surface antigen of the infectious stage of the parasite. Our major findings are that a subset of the CS message utilizes multiple polyadenylation sites, th at some processed CS transcripts are found in blood-stage parasites, a nd that the 5' untranslated region of the message is unusually long an d has multiple start sites. Moreover, repetitive motifs that may repre sent enhancers or transcriptional binding sites are present upstream o f the transcription unit. In addition, we describe details of the cDNA -directed PCR procedure that may be helpful to other parasitologists w ho work with small, unpurified biological samples.