HEAVY-ION MUTAGENESIS

选定的重离子已被证明是有效的诱变剂，在 两个不同遗传位点的人TK6淋巴母细胞：胸苷激酶 (TK)和次黄嘌呤磷酸核糖转移酶(Hgprt)。分子的动力学 突变诱导似乎依赖于基因背景 除LET外，还有特定的基因座。一项系统的调查研究 诱变效应与粒子电荷、速度和注量的关系 Hgprt半合子基因座和杂合子tk基因 轨迹。具体地说，诸如基因等考虑因素的假设 剂量和与必需基因的连锁不仅影响 诱导，以及对给定遗传位点的LET和RBE反应将 接受测试。其次，我们将确定突变率是否可能 对于相对于粒子的半合子轨迹，更容易饱和 对于杂合子基因座来说，这是一种不同的基因频率。这可能是由于 加速重离子诱发大规模遗传的倾向 变化，包括广泛的删除，以至于这些变化的规模 导致可存活突变的改变受到遗传连锁的限制。 这一假设将通过检查DNA结构的光谱来检验 Tk-/-或hgprt-突变体克隆衍生群体的变化 在暴露在单粒子束下的培养物中产生。基因内和 将检查多点变化以确定大小和极性 结构变化的影响。粒子注量对光谱的影响 将检查每个基因座的DNA结构变化。这种依赖 某一给定基因座的突变谱对人体吸收剂量的影响 还将对原子核进行探索。最后，神秘的可能性 与TK6细胞活性tk或hgprt等位基因连锁的致死等位基因 对可恢复突变体谱的影响将由 引入额外的17号染色体拷贝，其中包含 新霉素抗性转化含有大量缺失的TK6亚克隆 活动TK或HGPRT序列。Neo+回复到tk+，或回复到 HgPrt+将被重离子束重新诱变。DNA的光谱 NEO+/TK-或新建造的hgprt-line的结构更改将是 与野生型TK6的tk或hgprt突变体的比较 细胞暴露在相同的重离子束中。这些研究将 有助于我们理解遗传限制对 高密度电离诱变人体细胞的可能机制 辐射。

Selected heavy ions have been shown to be potent inducers of mutations in human TK6 lymphoblasts at two distinct genetic loci: thymidine kinase (tk) and hypoxanthine phosphoribosyltransferase (hgprt). The kinetics for mutation induction appear to depend on the genetic context of the particular locus in addition to LET. A systematic investigation of the dependence of mutation induction on particle charge, velocity and fluence is outlined for both the hemizygous hgprt locus and the heterozygous tk locus. Specifically, the hypothesis that considerations such as gene dosage and linkage to essential genes influence not only the kinetics of induction but also the LET vs RBE response for a given genetic locus will be tested. Secondly, we will determine whether the mutation rate may saturate more readily for a hemizygous locus with respect to particle fluence than for a heterozygous locus. This may be a result of the propensity with which accelerated heavy ions induce large scale genetic changes, including extensive deletions, such that the magnitude of those alterations resulting in viable mutants is limited by genetic linkage. This assumption will be tested by examining the spectrum of DNA structural alterations in clonally-derived populations of tk-/- or hgprt- mutants arising in cultures exposed to a single particle beam. Intragenic and multilocus change will be examined to determine the magnitude and polarity of structural alterations. The effect of particle fluence on the spectrum of DNA structural changes for each locus will be examined. The dependence of the mutation spectrum for a given locus on the absorbed dose to the nucleus will also be explored. Finally, the possibility that cryptic lethal alleles linked to the active tk or hgprt alleles of TK6 cells influence the spectrum of recoverable mutants will be examined by introducing an additional copy of chromosome 17 containing the gene for neomycin resistance into mutant TK6 subclones harboring large deletions of active tk or hgprt sequences. Neo+ revertants to tk+, or revertants to hgprt+ will be remutagenized with a heavy-ion beam. The spectrum of DNA structural alterations in neo+/tk- or newly made hgprt- lines will be compared with those obtained for tk- or hgprt- mutants of wild-type TK6 cells after exposure to the same heavy-ion beam. These studies will contribute to our understanding of the influence of genetic constraints on possible mechanisms of mutagenesis in human cell by densely ionizing radiations.