Fig. 3
From: The Rad51 paralogs facilitate a novel DNA strand specific damage tolerance pathway
The Shu complex promotes bypass of APOBEC3B-induced lesions. a APOBEC3B-induced mutation rates on the lagging strand of a replication fork measured using a CAN1 reporter integrated 16 kb from ARS216 on chromosome II. Expression of the cytidine deaminase APOBEC3B induces primarily lagging strand mutations caused by dU templated replication (G to A transition). The uracil glycosylase Ung1 removes U resulting in abasic site formation (AP) in the lagging strand, which can be bypassed by TLS (G to A transition, G to C transversion). b CSM2 and PSY3 are in the same pathway as UNG1 and their deletion results in similar mutation rates individually or in combination with each other. Mutation rates of the indicated genotypes were measured in CAN1 reporter strains transformed with either an empty or APOBEC3B-expressing vector. Error bars indicate 95% confidence intervals. c In the absence of CSM2 or PSY3, abasic sites accumulate and TLS predominates resulting in primarily G to A transitions (red) or G to C transversions (green) within the CAN1 locus. APOBEC3B expression in WT, ung1∆, or csm2∆ ung1∆ cells primarily result in G to A transitions. The rate reported represents the proportion of the CanR mutants observed from sequencing multiplied by the mutation rate determined in b. G to T substitutions are indicated in blue. Other mutations consisting of rare substitutions at A:T base pairs, insertions, deletions, and complex events composed of multiple mutations are depicted in purple. d The strand bias of CAN1 mutations from APOBEC3B expression was evaluated by Sanger sequencing. APOBEC3B expression results in a mutation bias in the lagging strand from templated replication of C deaminations. CSM2, PSY3, or UNG1 deleted cells exhibit more G mutations (green) than C mutations (red). Other mutations as defined in b are indicated in purple. Individual mutation rates were calculated as in c. Statistical significance of strand bias in APOBEC3B-expressing strains was determined by a two-tailed G-test with p < 0.05 for all genotypes
