Protein Interactions in Antibody Diversity

DNA聚合酶iota（Pol iota）因其保真度较低而成为抗体基因体细胞超突变的有吸引力的候选者。为了鉴定Pol i ota的作用，我们分析了两种酶缺陷的小鼠品系中的突变：129只小鼠具有可忽略的截短Pol i ota表达，以及敲入小鼠，其表达无催化活性的全长Pol i ota。两种菌株在可变区中具有正常的突变频率和谱，表明Poliota的缺失不改变总体诱变。然后，我们检查了Pol i ota是否影响由另一种易错聚合酶Pol zeta产生的串联突变。使用一种新的计算模型分析连续突变的频率，以确定它们是发生在单个DNA交易期间还是发生在两个独立事件期间。对来自两个品系的2，000个突变的分析表明，Pol 1 ta受损的小鼠失去了串联特征，而C57 BL/6小鼠积累了显著量的双突变。结果支持这样的模型，其中Pol i ota偶尔访问复制叉以产生第一突变，并且Pol zeta用第二突变扩展错配。

DNA polymerase iota (Pol iota) is an attractive candidate for somatic hypermutation in antibody genes because of its low fidelity. To identify a role for Pol iota, we analyzed mutations in two strains of mice with deficiencies in the enzyme: 129 mice with negligible expression of truncated Pol iota, and knockin mice which express full length Pol iota that is catalytically inactive. Both strains had normal frequencies and spectra of mutations in the variable region, indicating that loss of Pol iota did not change overall mutagenesis. We then examined if Pol iota affected tandem mutations generated by another error prone polymerase, Pol zeta. The frequency of contiguous mutations was analyzed using a novel computational model to determine if they occur during a single DNA transaction or during two independent events. Analyses of 2,000 mutations from both strains indicated that Pol iota-compromised mice lost the tandem signature, whereas C57BL/6 mice accumulated significant amounts of double mutations. The results support a model where Pol iota occasionally accesses the replication fork to generate a first mutation, and Pol zeta extends the mismatch with a second mutation.