Abstract
APOBEC3A/B cytidine deaminase is responsible for the majority of cancerous mutations in a large fraction of cancer samples. However, its role in heritable mutagenesis remains very poorly understood. Recent studies have demonstrated that both in yeast and in human cancerous cells, most of APOBEC3A/B-induced mutations occur on the lagging strand during replication and, on the non-template strand of transcribed regions. Here, we use data on rare human polymorphisms, interspecies divergence, and de novo mutations to study germline mutagenesis, and analyze mutations at nucleotide contexts prone to attack by APOBEC3A/B. We show that such mutations occur preferentially on the lagging strand and on non-template strands of transcribed regions. Moreover, we demonstrate that APOBEC3A/B-like mutations tend to produce strand-coordinated clusters, which are also biased towards the lagging strand. Finally, we show that the mutation rate is increased 3' of C→G mutations to a greater extent than 3' of C→T mutations, suggesting pervasive translesion bypass of the APOBEC3A/B-induced damage. Our study demonstrates that 20% of C→T and C→G mutations in the TpCpW context, where W denotes A or T, segregating as polymorphisms in human population, or 1.4% of all heritable mutations, are attributable to APOBEC3A/B activity.