Selective Metal Ion Utilization Contributes to the Transformation of the Activity of Yeast Polymerase η from DNA Polymerization toward RNA Polymerization.

Polymerase eta (Pol eta) is a translesion synthesis DNA polymerase directly linked to cancer development. It can bypass several DNA lesions thereby rescuing DNA damage-stalled replication complexes. We previously presented evidence implicating Saccharomyces cerevisiae Pol eta in transcription elongation, and identified its specific RNA extension and translesion RNA synthetic activities. However, RNA synthesis by Pol eta proved rather inefficient under conditions optimal for DNA synthesis. Searching for factors that could enhance its RNA synthetic activity, we have identified the divalent cation of manganese. Here, we show that manganese triggers drastic changes in the activity of Pol eta. Kinetics experiments indicate that manganese increases the efficiency of ribonucleoside incorporation into RNA by similar to 400-2000-fold opposite undamaged DNA, and similar to 3000 and similar to 6000-fold opposite TT dimer and 8oxoG, respectively. Importantly, preference for the correct base is maintained with manganese during RNA synthesis. In contrast, activity is strongly impaired, and base discrimination is almost lost during DNA synthesis by Pol eta with manganese. Moreover, Pol eta shows strong preference for manganese during RNA synthesis even at a 25-fold excess magnesium concentration. Based on this, we suggest that a new regulatory mechanism, selective metal cofactor utilization, modulates the specificity of Pol eta helping it to perform distinct activities needed for its separate functions during replication and transcription.