Figure 6.

Chromosomal circularization after DSB induction at IKI-L. HR2-L and HR2-R are two homologous regions sharing over 99% nucleotide identity along 1,672 bp and are symbolized as salmon pink boxes. The hybrid HR2 sequence is labelled HR2-L/R. HR3 is a region including two identical transposase encoding genes (SAM23877_7417 and SAM23877_7422) in opposite direction. Similarly, HR4 is a region including two identical transposase encoding genes (SAM23877_7326 and SAM23877_7404) in opposite direction. HR3 and HR4 are symbolized as purple boxes. Illegitimate recombination scars are represented by black wave lines. Green boxes represent inserted DNA stretches. Amplified sequences are marked out by light blue boxes between brackets. In some cases, circularization occurred by simple event of fusion between sequences present on both arms with (a) or without (b) DNA insertion. The other cases are typified by a common feature, which consists in the deletion of the left arm until the HR2-L locus and its recombination with its homologous region on the right arm (HR2-R), leading to the formation of a hybrid HR2-R/L sequence. This arm replacement is concomitant with circularization through different molecular event: HR involving HR3 or HR4 (c), IR (d) sometimes accompanied by DNA amplification (e) or DNA insertion (f). For case e, the read coverage level of the amplified region prevents the identification of the fusion sequence and thus the nature of the recombination event. For case (g), the circularization may have occurred through recombination between two short homologous sequences (41 bp) in opposite direction.