The dilute (d) coat color locus of mouse chromosome 9 has been identified by more than 200 spontaneous and mutagen-induced recessive mutations. With the advent of molecular probes for this locus, the molecular lesion associated with different dilute alleles can be recognized and precisely defined. In this study, two dilute mutations, dilute-lethal20J (dl20J) and dilute prenatal lethal Aa2, have been examined. Using a dilute locus genomic probe in Southern blot analysis, we detected unique restriction fragments in dl20J and Aa2 DNA. Subsequent analysis of these fragments showed that they represented deletion breakpoint fusion fragments. DNA sequence analysis of each mutation-associated deletion breakpoint fusion fragment suggests that both genomic deletions were generated by nonhomologous recombination events. The spontaneous dl20J mutation is caused by an interstitial deletion that removes a single coding exon of the dilute gene. The correlation between this discrete deletion and the expression of all dilute-associated phenotypes in dl20J homozygotes defines the dl20J mutation as a functional null allele of the dilute gene. The radiation-induced Aa2 allele is a multilocus deletion that, by complementation analysis, affects both the dilute locus and the proximal prenatal lethal-3 (pl-3) functional unit. Molecular analysis of the Aa2 deletion breakpoint fusion fragment has provided access to a previously undefined gene proximal to d. Initial characterization of this new gene suggests that it may represent the genetically defined pl-3 functional unit.

译文

小鼠9号染色体的稀释 (d) 毛色基因座已被200多个自发和诱变剂诱导的隐性突变鉴定。随着该基因座分子探针的出现,可以识别并精确定义与不同稀等位基因相关的分子病变。在这项研究中,已经检查了两个稀释的突变,dilute-lethal20J (dl20J) 和稀释的产前致死性Aa2。使用Southern印迹分析中的稀释基因座基因组探针,我们在dl20J和Aa2 DNA中检测到独特的限制性片段。对这些片段的后续分析表明,它们代表了缺失断点融合片段。对每个突变相关的缺失断点融合片段的DNA序列分析表明,两个基因组缺失都是由非同源重组事件产生的。自发性dl20J突变是由间隙缺失引起的,该间隙删除了稀基因的单个编码外显子。这种离散缺失与dl20J纯合子中所有稀相关表型表达之间的相关性将dl20J突变定义为稀基因的功能性空等位基因。辐射诱导的Aa2等位基因是多基因座缺失,通过互补分析,会影响稀释基因座和近端产前致死3 (pl-3) 功能单位。Aa2缺失断点融合片段的分子分析提供了接近d的先前未定义基因的途径。该新基因的初始表征表明它可能代表遗传定义的pl-3功能单元。

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