Nishino H, Buettner V L, Sommer S S
Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA.
Mutat Res. 1996 Nov 11;372(1):97-105. doi: 10.1016/s0027-5107(96)00172-8.
To explore further the origin of spontaneous mutations recovered with the Big Blue transgenic mouse mutagenesis assay, the spectrum of ex vivo mutations from pinpoint mutant plaques was determined and compared with the spectrum of putatively mouse-derived mutations from circular, mutant plaques. The entire lacI gene and lacZ operator region from 62 pinpoint blue plaques was sequenced. The observed mutational spectrum of pinpoint mutants differed significantly from that seen in circular mutants (p < 0.0001). Only four percent of the mutations were transitions at CpG sites whereas this type of mutation was the most common (35%) in circular mutants. Microdeletions/microinsertions were seen more frequently in pinpoint mutants relative to circular mutants. Four base pair deletion/insertion events at the E. coli hotspot tandem repeats were seen in 10 of 62 (16%) pinpoint mutants and minor hotspots of mutation were observed at bp 141 and 1110. The mutational spectrum of pinpoint mutants provides further evidence that most circular mutants originate in mouse.
为了进一步探究通过大蓝转基因小鼠诱变试验获得的自发突变的起源，测定了来自精确突变噬菌斑的体外突变谱，并与来自圆形突变噬菌斑的假定小鼠源性突变谱进行了比较。对62个精确蓝色噬菌斑的整个lacI基因和lacZ操纵区进行了测序。精确突变体的观察到的突变谱与圆形突变体中的显著不同（p < 0.0001）。只有4%的突变是CpG位点的转换，而这种类型的突变在圆形突变体中最为常见（35%）。相对于圆形突变体，微缺失/微插入在精确突变体中更频繁地出现。在62个精确突变体中的10个（16%）中观察到了大肠杆菌热点串联重复处的四个碱基对缺失/插入事件，并且在第141和1110碱基处观察到了次要突变热点。精确突变体的突变谱提供了进一步的证据，表明大多数圆形突变体起源于小鼠。
