Higher-order structure of interphase chromosomes and radiation-induced chromosomal exchange aberrations.

PURPOSE: To discuss the effects of chromosome structure on the inter- and intrachromosomal exchanges in the framework of the model, which argues that the higher-order chromosome structure contains 10-30 Mbp loop clusters (micelles).

RESULTS AND CONCLUSIONS: Intermicelle contacts determine exchange-type chromosome aberrations. Ratios of inter- to intrachromosomal exchanges calculated in the model are similar to the experimental data (literature) for human lymphocytes and flat fibroblasts. The frequency of interchanges is affected by nuclear shape; this might explain the greater number of interchanges observed in 3-D spherical lymphocytes vs. that in 2-D flat fibroblasts. Chromosome configuration (linear vs. folded Rab1) affects the pattern of micelle contacts. The model predicts that chromosomes in haploid Tradescantia microspores have the folded Rab1 orientation; this explains quantitatively the low value of the ratio of dicentrics to centric rings observed in these cells.