A plausible mechanism for large‐scale chromosomal DNA amplification in streptomycetes

Recent advances in our understanding of the structure of highly amplified DNA sequences in Streptomyces fradiae and lividans have enabled us to formulate a possible mechanism by which amplification may occur. An essential feature of the model is the generation of an amplification precursor, which comprises a circularised copy of the DNA to be amplified, attached to one arm of the chromosome by a replication fork. Multiple copies of the amplifiable DNA are generated by rolling circle replication. The model adequately accounts for many features of gene amplification in these two species, including the tendency for deletions to occur to one side, but not the other, of the amplified DNA.