Genetic alterations in γ-ray- and α-particle-induced HPRT mutants were examined by multiplex polymerase chain reaction (PCR) analysis. A total of 39-63% of γ-ray-induced and 31-57% of α-particle-induced mutants had partial or total deletions of the HPRT gene. The proportion of these deletion events was dependent on radiation dose, and at the resolution limits employed there were no significant differences between the spectra induced by equitoxic doses of α particles (0.2-0.4 Gy) and γ rays (3 Gy). The molecular nature of the deletions was analyzed by the use of sequence tagged site (STS) primers and PCR amplification as a "probe" for specific regions of the human X chromosome within the Xq26 region. These STSs were closely linked and spanned regions approximately 1.7 Mbp from the telomeric side and 1.7 Mbp from the centromeric side of the HPRT gene. These markers include: DXS53, 299R, DXS79, yH3L, 3/19, PR1, PR25, H2, yH3R, 1/44, 1/67, 1/1, DXS86, D8C6, DXS10 and DXS144. STS analyses indicated that the maximum size of total deletions in radiation-induced HPRT mutants can be greater than 2.7 Mbp and deletion size appears to be dependent on radiation dose. There were no apparent differences in the sizes of the deletions induced by α particles or γ rays. On the other hand, deletions containing portions of the HPRT gene were observed to be 800 kbp or less, and the pattern of the partial deletion induced by α particles appeared to be different from that induced by γ rays.

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