摘要：In this work we have constructed a plasmid to compare intraplasmid recombination efficiency in Agrobacterium tumefaciens and Escherichia coli. The plasmid contains two directly repeated copies of spectinomycin resistance gene, one lacking 5’ and the other lacking 3’ end. These two copies share a 570-bp region of homology and are separated by the ampicillin resistance gene. Homologous recombination between repeated copies of incomplete spectinomycin resistance genes results in the restoration of spectinomycin resistance. During this process, ampicillin resistance gene is either deleted or incomplete spectinomycin genes are amplified along with the ampicillin resistance gene. This experimental system enabled us to follow for the first time the generation of deletions and amplifications during intraplasmid recombination in A. tumefaciens. We show here that predominantly RecA-independent mechanism contributes to the formation of deletion and amplification products in both, A. tumefaciens and E. coli. Additionally, deletion and amplification products were detected at similar frequencies, suggesting that amplifications and deletions probably occur by a similar mechanism.
