Molecular biology of mutagenesis of mammalian cells by ionizing radiation.

In mammalian cells, ionizing radiation induces comparable numbers of point mutations (principally base changes, frameshifts and small deletions) and of large deletions of more than a hundred base pairs. The latter are formed either by misrepair of an end from one double-strand break with an end from another, or by a second mechanism which, it is suggested, is initiated by slowly repaired single-strand nicks. The ratio of deletions to point mutations is variable from one gene to another, and is greatest for genes in which very large deletions still allow cells to survive.