The chromosome territory of human oncogenes.

The prevailing view of the chromosome of higher organisms is characterized by randomness. Genes are believed to be located at random and mutations and most structural rearrangements are likewise supposed to occur at random (1-4). During the last few years the molecular organization of the eukaryotic chromosome has been subject to intensive investigation but the evidence has been mainly on single DNA sequences and their immediate neighbours. Most molecular findings, such as the split gene, the pseudo-genes, the transposable elements, and the enhancers, are relatively short DNA sequences and do not furnish information on the organization of the large structure that is the eukaryotic chromosome considered as a whole. It is the relative position of DNA segments within the chromosome as a unit that is the subject of this paper. Every chromosome arm is well delimited by a centromere and a telomere. It has been established long ago that chromosome arms cannot survive without centromeres and without telomeres (5). An extensive analysis of the position of specific DNA segments in a wide number of species has shown that their position within the chromosome arm is related to the location of the two main regions: the centromere and the telomere. These results led to the concept of the chromosome field (6-8). The validity and usefulness of this approach has been shown by the fact that it has led to predictions on gene location and gene function. An example is the location of the genes for 28S and 18S ribosomal RNA that can be predicted within reasonable limits independently of the phylogenetic position of a species and of the length of a chromosome. An analysis of 165 species (including plants, worms, amphibians and humans) showed that the ribosomal DNA sequences display two organizatory features: (i) In 90.5~ of the cases they are located in the short arm, i.e., the one in which the number of nucleotide pairs between the centromere and the telomere is lowest and