THE GENE DISTRIBUTION OF THE MAIZE GENOME

Previous investigations from our laboratory showed that the genomes of plants, like those of-vertebrates, are mosaics of isochores, i,e., of very long DNA segments that are compositionally homogeneous and that can be subdivided into a small number of families characterized by different GC levels (GC is the mole fraction of guanine + cytosine). Compositional DNA fractions corresponding to different isochore families were used to investigate, by hybridization with appropriate probes, the gene distribution in vertebrate genomes. Here we report such a study on the genome of a plant, maize. The gene distribution that we found is most striking, in that almost all genes are present in isochores covering an extremely narrow (1-2%) GC range and only representing 10-20% of the genome, This gene distribution, which seems to characterize other Gramineae as well, is remarkably different from the gene distribution previously found in vertebrate genomes.