Abstract: Homologous recombination plays a critical role in maintaining genetic diversity as well as genome stability. Interesting examples implying hyper-recombination are found in nature. In chloroplast DNA (cpDNA) and the herpes simplex virus 1 (HSV-1) genome, DNA sequences flanked by inverted repeats undergo inversion very frequently, suggesting hyper-recombinational events. However, mechanisms responsible for these events remain unknown. We previously observed very frequent inversion in a designed amplification system based on double rolling circle replication (DRCR). Here, utilizing the yeast 2-mum plasmid and an amplification system, we show that DRCR is closely related to hyper-recombinational events. Inverted repeats or direct repeats inserted into these systems frequently caused inversion or deletion/duplication, respectively, in a DRCR-dependent manner. Based on these observations, we suggest that DRCR might be also involved in naturally occurring chromosome rearrangement associated with gene amplification and the replication of cpDNA and HSV genomes. We propose a model in which DRCR markedly stimulates homologous recombination.CI - (c) 2011 The Authors. Journal compilation (c) 2011 by the Molecular Biology Society of Japan/Blackwell Publishing Ltd.