Why Does E. coli have Three Translesion Synthesis DNA Polymerases

Why Does E. coli have Three Translesion Synthesis DNA Polymerases [126, 127]  

Although Pol V replicates undamaged templates with relatively low fidelity (10 3 to 10-4) [76], one striking quality is Pol V s ability to accurately bypass UV photoproducts (e.g., inserting dATP opposite thymine-thymine (TT) cyclobutane pyrimidine dimers (CPDs) [76]). Analysis of insertion tendencies opposite a variety of adducts/lesions led to the observation that Pol V seems to have two insertion modes (i) correct dNTP insertion and (ii) default dATP insertion [37]. UV light is a frequently encountered form of DNA damage for which a translesion synthesis DNA polymerase might be important and since TT CPDs are the major UV lesion 

Pol IV replicates undamaged DNA only around 5-fold less accurately than the catalytic a-subunit of Pol III [76]. It is prone to making -1 frameshift mutations in homopolymeric runs of six or more GC base pairs base substitutions also result (18-30%) [71, 90]. However, Pol IV s most striking quality is its ability to accurately 

The translesion synthesis DNA polymerases also confer selective advantage on E. coli during long periods in stationary phase-the growth advantage in stationary phase (GASP) phenotype [97]. Finally, Pol IV is particularly elevated in stationary phase (around 7500/cell) and is implicated in adaptive mutagenesis [98]. 

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