CHROMOSOMAL RADIOSENSITIVITY AT INTRACHROMOSOMAL TELOMERIC SITES

Telomeric DNA is composed of highly conserved sequences which are pres ent at the termini of chromosomes as well as at intrachromosomal locat ions. Here, we studied a Chinese hamster ovary (CHO) cell line, BL-10, with highly stable amplified telomeric DNA at the termini as well as at intrachromosomal locations. We show that intrachromosomal or inters titial telomeric sites in this cell line and in another CHO cell line, HA- 1, are radiosensitive in that they are more prone to breakage tha n would be expected based on the percentage of the genome composed of telomeric sequences. The frequency of breakage at interstitial telomer ic sites is 4.3 to &3 times higher than that in the CHO genome overall . These conclusions are reached by both conventional cytogenetic analy sis of two CHO cell lines which have the same survival rates after exp osure to ionizing radiation, and by use of double fluorescence in situ hybridization (FISH) with a pan-telomere-specific probe and a CHO chr omosome-specific library in the same metaphase cells after irradiation . (C) 1993 Wiley-Liss, Inc.