Replication Protein A (RPA70C) Negatively Regulates Ribonucleotide Reductase (RNR) in the model plant \u3cem\u3eArabidopsis thaliana\u3c/em\u3e

Replication protein A (RPA) is a heterotrimeric single-stranded DNA-binding protein that plays an important role in cellular responses to DNA damage. For example, RPA can activate the cell-cycle checkpoint protein ATR in the presence of persisting DNA damage. The model plant Arabidopsis thaliana has 5 functional homologous RPA70 genes which may play specific roles in response to DNA damaging agents. One chemical that causes DNA damage in Arabidopsis is Hydroxyurea (HU), which blocks DNA replication by inhibiting activity in Ribonucleotide Reductase (RNR), an enzyme responsible for the production of free deoxyribonucleotides (dNTPs). In studies of Arabidopsis mutants, atr plants, but not rpa70c, were found to be hypersensitive to HU and had inhibited root and shoot growth and increased root hair formation. However, the double mutant rpa70c.atr was found to be less sensitive to HU and had an enhanced expression of RNR compared to atr single mutants. The double mutant\u27s curious phenotype indicates that the double mutant suppresses the phenotype of the atr mutation and that the absence of the RPA70C gene partially reverses the effect of HU on atr mutant plants, probably due to the enhanced expression of RNR. These results indicate that RPA70C in conjunction with ATR plays a role in the regulation of DNA replication