The genome of Schistosoma mansoni: Isolation of DNA, its size, bases and repetitive sequences

DNA has been prepared from adults and cercariae of Schistosoma mansoni utilizing a technique that involves centrifugation through cesium chloride. The DNA isolated from S. mansoni adults and that isolated from cercariae were found to be indistinguishable in all analyses. No modified bases were detected by chromatography or comparative endonuclease restriction. C o t analysis demonstrated that the haploid genome of S. mansoni is 0.26 pg (2.7 × 10 8 base pairs) and that the genome contains both moderately and highly repeated components. Some of the repetitive fraction of DNA consists of tandemly repeated ribosomal genes of which there are 500–1000 copies per genome (1.8–3.6% of the total DNA). Four other non-ribosomal repetitive sequences (comprising at least a further 2.0% of the total DNA) have been isolated from a DNA clone bank and their arrangement within the S. mansoni genome investigated by restriction and Southern blot analysis. These cloned segments of DNA appear in many different locations within the genome and thus are reminiscent of the interspersed DNA sequences described in higher eukaryotic organisms.