Ataxia telangiectasia resists gene cloning: an account of parameters determining gene transfer into human recipient cells.

A subclone of an SV40-transformed fibroblast cell line from a patient with Ataxia telangiectasia (AT) with a relatively high rate of DNA uptake was isolated. However, more than 65000 independent genomic transfectants (using wild-type human DNA) did not contain the functional AT gene. This number represents the statistical distribution of an amount of DNA equivalent to more than three times the haploid human genome. The transfectants were screened by an X ray selection protocol that could rescue a single wild-type cell out of a population of 10(6) AT cells. This suggests a reversion frequency for AT of below 10(-8). The DNA uptake into human cells is compared with that into NIH3T3 cells and future possibilities for the isolation of human repair genes are discussed.