Plant & Animal Genome V Conference
Town & Country Hotel, San Diego, CA, January 12-16, 1997.
PAG-V: S21 - GENE DISTRIBUTION IN ANIMALS AND PLANTS
S21
GENE DISTRIBUTION IN ANIMALS AND PLANTS
BERNARDI, GIORGIO
Laboratoire de Génétique Moléculaire, Institut Jacques Monod, 2 Place Jussieu, 75005 Paris, France.
A review of our present knowledge on the different distributions of genes in the genomes of vertebrates and angiosperms will be
presented. The differences are exemplified by findings concerning the human and the maize genomes. The human genome is a mosaic of
isochores, long (>300 kb) DNA segments, which are compositionally homogeneous and can be divided into a small number of families
characterized by different GC levels covering a 30-60 % range. Isochore families L1, L2 and H1, H2, H3 represent the GC-poor 2/3 and the
GC-rich 1/3 of the genome, respectively. The distribution of genes in the human genome is strikingly non-uniform. Indeed, a low gene
concentration is present in the GC-poor isochore families L1 and L2; gene concentration then increases in increasingly GC-rich isochores
(isochore families H1 and H2) to attain the highest value (20x higher than in L1+L2) in the GC-richest isochore family H3 (the 'genome core'),
that only represents about 4% of the genome. Because isochore distribution in chromosomes is known, these results also provide information
on the distribution of genes in chromosomes. The maize genome has about the same size as the human genome, and is also made up of
isochores covering a 30-65% GC range. Its gene distribution is, however, very different from that of the human genome in that almost all genes
are present in isochores covering an extremely narrow GC range (1-2%) representing 10-20% of the genome, the 'gene space'. The meaning of
the different gene distributions of angiosperms and vertebrates will be discussed along with the practical implications of the compositional
fractionation of genomes.