Genetics, Vol 136, 857-865, Copyright © 1994


INVESTIGATIONS

The Small Ribosomal Subunit RNA Isoforms in Plasmodium cynomolgi

V. Corredor and V. Enea
Present address: Department of Cell Biology and Anatomy, Box 1007, Mount Sinai Medical Center, One Gustave L. Levy Place, New York, NY 10029-6574.

We report the isolation, characterization and analysis of the small subunit rRNA genes in Plasmodium cynomolgi (Ceylon). As in other Plasmodium species, these genes are present in low copy number, are unlinked and form two types that are distinct in sequence and are expressed stage specifically. The asexually expressed (type A) genes are present in four copies in the Ceylon(-) and in five copies in the Berok(-) strain. Surprisingly, the sexually expressed (type B) gene is present in a single copy. The vast majority of the differences between gene types is confined to the variable regions. The pattern of divergence is different from that observed in Plasmodium berghei or in Plasmodium falciparum. Analysis of the small subunit rRNA sequences of P. cynomolgi, P. berghei and P. falciparum, indicates that the two gene types do not evolve independently but rather interact (through gene conversion or some form of recombination) to such an extent as to erase whatever stage-specific sequence signatures they may have had in the last common ancestor.


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