Intrachromosomal localization of breakpoints induced by the restriction endonucleases Alu I and Bam HI in Chinese hamster ovary cells treated in S phase of the cell cycle

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Abstract
The restriction endonucleases (REs) Alu I and Bam HI were electroporated into Chinese hamster ovary (CHO) cells during S phase of the cell cycle and breakpoints in G-banded metaphases were mapped to Giemsa-light ordark bands or to band junctions. The majority of Alu I- and Bam HI-induced breakpoints were located in Giemsa-light bands. Both REs induced similar distributions of breakpoint clusters. The localization pattern of S phase-induced breakpoints in CHO cells is similar to the pattern of G 1-induced breakpoints reported earlier. These data show that breakpoint localization for both REs is independent of the cell cycle stage (G 1 or S) in which aberrations are induced and give further support to the hypothesis that nuclease hypersensitive regions (NHRs) associated with active genes play an important role in the distribution of breakpoints.