Yeast DNA polymerase ζ maintains consistent activity and mutagenicity across a wide range of physiological dNTP concentrations

In yeast, dNTP pools expand drastically during DNA damage response. We show that similar dNTP elevation occurs in strains, in which intrinsic replisome defects promote the participation of error-prone DNA polymerase zeta (Pol zeta) in replication of undamaged DNA. To understand the significance of dNTP pools increase for Pol zeta function, we studied the activity and fidelity of four-subunit Pol zeta (Pol zeta(4)) and Pol zeta(4)-Rev1 (Pol zeta(5)) complexes in vitro at 'normal S-phase' and 'damage-response' dNTP concentrations. The presence of Rev1 inhibited the activity of Pol zeta and greatly increased the rate of all three 'X-dCTP' mispairs, which Pol zeta(4) alone made extremely inefficiently. Both Pol zeta(4) and Pol zeta(5) were most promiscuous at G nucleotides and frequently generated multiple closely spaced sequence changes. Surprisingly, the shift from 'S-phase' to 'damage-response' dNTP levels only minimally affected the activity, fidelity and error specificity of Pol zeta complexes. Moreover, Pol zeta dependent mutagenesis triggered by replisome defects or UV irradiation in vivo was not decreased when dNTP synthesis was suppressed by hydroxyurea, indicating that Pol zeta function does not require high dNTP levels. The results support a model wherein dNTP elevation is needed to facilitate nonmutagenic tolerance pathways, while Pol zeta synthesis represents a unique mechanism of rescuing stalled replication when dNTP supply is low.