SINGLE-COPY SEQUENCE HOMOLOGY AMONG THE GC-RICHEST ISOCHORES OF THE GENOMES FROM WARM-BLOODED VERTEBRATES

We have hybridized a human DNA fraction corresponding to the GC-riches t and gene-richest isochore family, H3, on compositional fractions of DNAs from 12 mammalian species and three avian species, representing e ight and three orders, respectively. Under conditions in which repetit ive sequences are competed out, the H3 isochore probe only or predomin antly hy bridized on the GC-richest fractions of main-band DNA from al l the species investigated. These results indicate that single-copy se quences from the human H3 isochores share homology with sequences loca ted in the compositionally corresponding compartments of the vertebrat e genomes tested. These sequences are likely to be essentially formed by conserved coding sequences. The present results add to other lines of evidence indicating that isochore patterns are highly conserved in warm-blooded vertebrate genomes. Moreover, they refine recent reports (Sabeur et al., 1993; Kadi et al., 1993), and correct them in some det ails and also in demonstrating that the shrew genome does not exhibit the general mammalian pattern, but a special pattern.