[Gene amplification in prokaryote and eukaryote systems]

The studied cases of gene amplification in bacteriophages, bacteria, yeasts, Drosophila, animal viruses and animal cells are reviewed. It is suggested that gene amplification is the mechanism universal for all classes of organisms and necessary for: 1) rendering the needed overhigh level of gene expression provided that the efficiency of the given gene transcription reaches in maximum (adaptive amplification), 2) preferential genome replication in case the efficiency of replication initiation reaches its maximum (competitive amplification), 3) rendering the essential stable DNA-protein interaction, if this interaction is damaged by DNA deletion (compensatory amplification). Molecular mechanisms for gene amplifications are: a) multiple sequential gene duplications, b) differential overreplication, excision, extrareplication and reintegration.