HEAVY-ION MUTAGENESIS

选定的重离子已被证明是突变的有效诱导剂， 人TK 6淋巴母细胞两个不同基因位点：胸苷激酶 (tk)和次黄嘌呤磷酸核糖基转移酶（HGPRT）。 的动力学 突变诱导似乎取决于遗传背景的 除了LET之外，还有特定的轨迹。 系统地调查了 突变诱导对粒子电荷、速度和注量的依赖性 概述了半合子hgprt基因座和杂合子tk 基因座 具体来说，假设考虑因素，如基因 剂量和与必需基因的联系不仅影响 诱导，而且对于给定的遗传基因座的LET与RBE反应将 得到考验 其次，我们将确定突变率是否可能 相对于颗粒，半合子位点更容易饱和 比杂合基因座的通量更大。 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，这样的幅度， 导致可存活突变体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。 克隆衍生的tk-/-或hgprt-突变体群体的改变 在暴露于单粒子束的培养物中产生。 基因内和 将检查多位点变化以确定大小和极性 的结构性变化。 粒子注量对光谱的影响 将检查每个位点的DNA结构变化。 的依赖 的突变谱为一个给定的位点上的吸收剂量， 核也将被探索。 最后，神秘的 与TK 6细胞的活性tk或hgprt等位基因连锁的致死等位基因 可恢复突变体谱的影响将通过以下方式进行检查： 引入含有以下基因的染色体17的额外拷贝： 新霉素抗性突变TK 6亚克隆携带大缺失的 活性TK或HGPRT序列。 Neo+回复突变为tk+，或回复突变为 将用重离子束再诱变hgprt+。 DNA的光谱 neo+/tk-或新制造的hgprt-系的结构改变将 与野生型TK 6的tk-或hgprt-突变体相比， 细胞暴露于相同的重离子束后。 这些研究将 有助于我们理解基因限制对 高密度电离辐射致人细胞突变的可能机制 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.