A rational approach to the serial culture of malaria parasites: evidence for a deficiency in RNA synthesis during the first cyclein vitro

Abstract

When ring-stage parasites are grown to the late trophozoite stagein vitro, the incorporation of [3H]adenosine into parasite DNA and RNA is in the ratio of ~ 1:1·5 and not 1:4 as expected from direct biochemical analysis of the parasite. A method is described by which large quantities of infected blood can be grownin vitrofrom the ring to the trophozoite stage thus allowing direct biochemical analysis of parasites grownin vitro. The results of direct biochemical analysis indicated that parasites grownin vitrohave similar DNA and protein contents to those grownin vitrobut that RNA contents are much lessin vitro. Quantitative histochemical studies also indicated a deficiency in RNA in parasites grownin vitro. It is concluded from the evidence of three distinct methods that RNA synthesis is defective during the first asexual cyclein vitro. In the second cycle all three macromolecular biosyntheses studied are reduced when compared to the first so that the actual rate of RNA synthesis is further reduced when compared to thatin vitro. It is suggested that the successive decrease in RNA synthesis parallels the reduction in multiplication obtained on subculture of the parasite.