Mutations induced in the HPRT gene by X-irradiation during G1 or S: analysis of base pair alterations, small deletions, and splice errors

Abstract Reverse transcriptase PCR was performed with mRNA obtained from HPRT mutants that had base pair alterations, or small deletions or insertions 1 or S (3–4-fold higher for 6 than 3 Gy). However, the frequencies of mutants that did not yield RT-PCR products were ∼10-fold higher in the cells irradiated in G 1 than in those irradiated in S. Sequence analysis of RT-PCR products and genomic DNA showed that 40% of the RT-PCR products had splice errors (one or more exons not spliced into mRNA), with 64% of them due to 1–17 bp deletions. Also, the distributions of molecular alterations in exons, acceptor sites, and donor sites for mutants having splice errors (observed in this study and reported by others) were similar to those reported for mutants not yielding RT-PCR products (isolated from Russian cosmonauts). In addition, we have found previously that large deletions which eliminated 1–9 exons were preferentially induced in G 1 . Therefore, we postulate that the preferential induction of mutants not yielding mRNA is due primarily to splice errors that result from deletions preferentially induced during G 1 . These splice errors would then result either in no message or a message that is rapidly degraded.