Ribonucleic acid synthesis in Plasmodium knowlesi maintained both in vivo and in vitro.

RNA extracted from purified parasites of Plasmodium knowlesi was fractionated using agarose gel electrophoresis. Preparations from para sites grown both in vivo and in vitro contained species of RNA with sedimentation coefficients of 4-0S, 5-0S, 16-6S, 24-2S, 31-4S, 38-0S and 48-3S. There was less RNA present in parasites grown in vitro than the equivalent stage parasites grown in vivo but the proportional amounts of the various species of RNA was similar in both cases. It is suggested that the 24-2S and 16-6S species of RNA are ribosomal and that the high molecular weight 31-4S, 38-0S and 48-0S species are ribosomal precursors. Ribosomal RNA synthesis occurs throughout the cell cycle during growth from the ring to the schizont stage; maximum incorporation of [H3]-adenosine occurs at the late trophozoite stage before nuclear division.