The prometaphase bands of human chromosomes: compositional features and gene distribution

Abstract

The human genome is a mosaic of long, compositionally homogeneous DNA segments, the isochores, that can be partitioned into five families. Two GC-poor families (LI and L2) representing 63% of the genome, and three GC-rich families (H1, H2 and H3) representing 24%, 7.5% and 4-5% of the genome, respectively [1]. Gene concentration increases with increasing GC levels, and reaches a 20-fold higher level in H3 compared to L isochores [2].In situhybridization of DNA from different isochore families provides, therefore, information on the chromosomal distribution of genes. Using this approach, three subsets of R(everse) or G(iemsa)-negative bands, H3+, H3*and H3-, containing large, moderate, and no detectable amounts, respectively, of the gene-richest H3 isochores were identified at a resolution of 400 bands [3]. H3+bands largely overlap with the most heat-denaturation-resistant bands [4], the chromomycin-A3-positive, 4,6-diamindino-2-phenylindole (DAPI)-negative bands [5], the bands with the highest CpG island concentrations [6], and the earliest replicating bands [7]. Here we have defined the H3+bands at a 850-band resolution, and have thus identified the human genome regions, having an average size of 4 Mb, that are endowed with the highest gene density.KeywordsHuman ChromosomeNegative BandCytogenet CellColor PlateBand ResolutionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.