Abstract
Quasipalindromes (QPs) are inverted DNA repeats with asymmetrical elements. These regions are hotspots for a particular class of template switch mutation, termed quasipalindrome mutagenesis (QPM) which converts the quasipalindrome to a more perfect palindrome. In this work, we employ an engineered reporter system to directly measure the frequency of QPM events. We compare the dynamics of these events in the contexts of double-strand break repair and normal replication. Through a genetic approach we identify mismatch repair and transcription-coupled nucleotide excision repair as primary mechanisms by which cells avoid QPM events. Previous work identified DNA-protein crosslinkers as inducers of QPM in E. coli. We demonstrate that multiple DNA-protein crosslinkers induce QPM in budding yeast. In this context we screen a variety of genes for roles in prevention of DPC-induced QPM. We also identify strand-specificity in yeast QPM, determining that these events are more likely during first-strand synthesis of DSB repair and when replicating the transcribed strand of genes. Together this work represents a systematic genetic study of QPM in yeast, which describes agents that promote this unique class of mutation as well as mechanisms by which cells maintain genomic fidelity at these regions.