Acinetobacter baumannii encodes multiple mutagenically and biochemically active DNA polymerase V variants

Acinetobacter baumannii natural isolates encode multiple copies of E. coli DNA polymerase V (pol VEc) umuDC homologs, some with as many as four nonidentical umuC and three nonidentical umuD genes encoding twelve possible pol VAb variants. Here, we show that six of the twelve pol VAb drive spontaneous and methyl methanesulfonate-induced mutations when expressed in E. coli. Mutagenesis depends on co-expression with RecAAb. Five mutagenically active pol VAb combinations assemble in vitro as stable mutasome complexes that synthesize DNA, pol VAb Mut = UmuD'2CAb-RecAAb-ATP/ATPγS. One of the mutasomes requires an A. baumannii-encoded β/τ processivity clamp for activity in vitro. Translesion DNA synthesis (TLS) occurs at T^T cyclobutane dimers, with different variants exhibiting different nucleotide misincorporation specificities. As observed for E. coli pol V and R391 ICE-encoded Rum pol, a single amino acid substitution in RecA, RecAAb M196D, abolishes A. baumannii pol V-induced mutagenesis.