The genome of Plasmodium cynomolgi is partitioned into separable domains which appear to differ in sequence stability

The genome of Plasmodium cynomolgi is partitioned into at least 7 distinct genetic domains. Each domain is apparently uniform in DNA density and is separable from the others by CsCl density centrifugation in the presence of Hoechst dye. The protein-encoding genes that were tested are localized in the two heaviest density domains (isochores). The ribosomal genes are in two lighter isochores as well as in one of the isochores that contains protein encoding genes. Telomeric sequences are mainly, if not exclusively, in the lightest isochores, indicating that position with regard to chromosome ends may correlate with density. Blocks of a tandemly-repeating sequence which mark genetically hypervariable chromosome regions in malaria parasites are located in all isochores. However, the rate of change associated with the blocks of sequence is much slower in some isochores than in others. This indicates that the rate of genetic change in these parasites may differ with isochore and chromosomal position. These results may also have more general biological implications since they suggest that the genetic instability often noted for tandem repeat sequences in the eukaryotic genome may be limited to only a distinct subset of the genomic complement of such sequence blocks.