de Serres F J, Brockman H E, Overton L K
Center for Life Sciences and Toxicology, Research Triangle Institute, Research Triangle Park, NC 27709.
Mutat Res. 1991 Aug;253(1):21-32. doi: 10.1016/0165-1161(91)90342-6.
The mutagenicity of 2-amino-N6-hydroxyadenine (AHA) has been studied in Neurospora crassa by treating a two-component heterokaryon (H-12) and recovering specific-locus mutations induced in the ad-3 region. This assay system permits the identification of ad-3A and/or ad-3B mutants resulting from gene/point mutations, multilocus deletion mutations, and multiple-locus mutations of various genotypes, involving one or both loci. Genetic characterization of the ad-3 mutants recovered from experiments with AHA in H-12 shows that 98.9% (270/273) of the ad-3 mutants are gene/point mutations (ad-3R), 1.1% (3/270) are unknowns, and none is a multilocus deletion mutation (ad-3IR). Among the gene/point mutations, 3.3% (9/273) are multiple-locus mutations (gene/point mutations with a closely-linked recessive lethal mutation [ad-3R + RLCL]). Another 25.3% (69/273) are multiple-locus mutations with a recessive lethal mutation located elsewhere in the genome [ad-3R + RL]. Heterokaryon tests for allelic complementation among the ad-3BR mutants showed that 90.8% (139/153) of the mutants were complementing, and 20.3% (31/153) were leaky. In addition, 32.5% (38/117) of the ad-3AR mutants were leaky. These data are consistent with the hypothesis that AHA produces specific-locus mutations in the ad-3 region of N. crassa by base-pair substitution. The data from the present experiments are compared with the data for 2-aminopurine (2AP)-induced ad-3 mutants in H-12 (de Serres and Brockman, 1991). Whereas, 2AP is a weak mutagen in H-12, AHA is extremely potent (Brockman et al., 1987). In contrast with 2AP, AHA induces ad-3 mutants exclusively by gene/point mutation in H-12. We conclude that whereas AHA induces ad-3 mutants predominantly by AT to GC base-pair transitions, 2AP induces ad-3 mutants by a wide variety of mechanisms including: (1) AT to GC and GC to AT base-pair transitions, (2) frameshift mutations, (3) other, as yet unidentified, intragenic alterations, (4) small multilocus deletion mutations, and (5) multiple-locus ad-3R mutations with closely linked recessive lethal mutations.
通过处理双组分异核体（H-12）并回收在ad-3区域诱导的特定位点突变，对2-氨基-N6-羟基腺嘌呤（AHA）在粗糙脉孢菌中的致突变性进行了研究。该检测系统能够鉴定由基因/点突变、多位点缺失突变以及各种基因型的多位点突变（涉及一个或两个位点）产生的ad-3A和/或ad-3B突变体。从H-12中用AHA进行的实验回收的ad-3突变体的遗传特征表明，98.9%（270/273）的ad-3突变体是基因/点突变（ad-3R），1.1%（3/270）是未知类型，没有一个是多位点缺失突变（ad-3IR）。在基因/点突变中，3.3%（9/273）是多位点突变（带有紧密连锁隐性致死突变的基因/点突变[ad-3R + RLCL]）。另外25.3%（69/273）是在基因组其他位置带有隐性致死突变的多位点突变[ad-3R + RL]。对ad-3BR突变体之间的等位基因互补进行的异核体测试表明；90.8%（139/153）的突变体具有互补性，20.3%（31/153）是渗漏型。此外，32.5%（38/117）的ad-3AR突变体是渗漏型。这些数据与AHA通过碱基对替换在粗糙脉孢菌的ad-3区域产生特定位点突变的假设一致。将本实验的数据与H-12中2-氨基嘌呤（2AP）诱导的ad-3突变体的数据（de Serres和Brockman，1991）进行了比较。虽然2AP在H-12中是一种弱诱变剂，但AHA极具诱变力（Brockman等人，1987）。与2AP不同，AHA在H-12中仅通过基因/点突变诱导ad-3突变体。我们得出结论，虽然AHA主要通过AT到GC的碱基对转换诱导ad-3突变体，但2AP通过多种机制诱导ad-3突变体，包括：（1）AT到GC和GC到AT的碱基对转换，（2）移码突变，（3）其他尚未确定的基因内改变，（4）小的多位点缺失突变，以及（5）带有紧密连锁隐性致死突变的多位点ad-3R突变。
