Repeat sequence instability is not closely linked to unique sequence instability in X-irradiated HT1080 (HPRTdup) cells

Abstract

Although radiation-induced genomic instability has been demonstrated by the use of repeat sequence instabilities in most cases, little is known about its association with mutations at ordinary protein-coding genes. We introduced partial duplication within the HPRT gene (HPRT^dup) in human cells (HT1080), which can measure mutation rates at repeat and unique sequences in the same HPRT gene locus. Namely, the HPRT^dup cells are HPRT(-), hence 6TG resistant, while deletion of one of the duplicated sequences by recombination makes the cells HPRT(+), hence HAT resistant. Further, the revertants can be subjected to forward mutation assay using 6TG resistance as the marker. >From X-irradiated HPRT^dup cell pools, we have isolated a large number of clones that showed elevated reversion rates by 10 to 100-fold as a result of delayed mutation. Following measurements of forward mutation rate in each clone, we found that the two mutaion rates do not always correlate.