Julianna Cresti

Mentor: Simmons
Molecular, Cellular & Developmental Biology

Areas of Interest

Ribonucleotides are a lot more abundant in the genome than we might think — for 1 round of replication in E. coli, 2000 ribonucleotide monophosphates are incorporated by DNA polymerase III in the place of their cognate deoxyribonucleotides. Replicative DNA polymerases are biased in their selection of nucleotides, despite their own innate selectivity mechanisms, because there are 100-1000 times more ribonucleotides than deoxyribonucleotides in the cell at any given time. These sugar errors, marked by the difference of a 2’ hydroxyl group, have the potential to destabilize and corrupt the genome downstream via induction of double-stranded breaks (DSBs) and may even be lethal. Naturally, the cell has built-in repair mechanisms for such errors. The Ribonuclease H (RNase H) family of proteins, whose common function is to resolve RNA incorporated in DNA, are found in all kingdoms of life. Bacillus subtilis, the Gram-positive model bacterium, is the only known organism that expresses all three family members: Ribonuclease HI (RNase HI), Ribonuclease HII (RNase HII), and Ribonuclease HIII (RNase HIII). Uniquely, RNase HII can resolve the aforementioned single sugar errors in a pathway called Ribonucleotide Excision Repair (RER). Although this pathway is known, it remains to be fully explored in bacteria, and particularly in Gram-positive bacteria, which have some fundamental differences from their Gram-negative counterparts, like E. coli. In humans, mutations in RNase HII result in a severe autoimmune disease called Aicardi-Goutières syndrome (AGS), which appears as early as infancy. B. subtilis provides us with a unique model system to explore the activity and substrate specificity of RNase HII both in vitro and in vivo, as well as its spatiotemporal distribution in the cell, in the context of all three RNase H family proteins so that we can better understand how genomic information is faithfully transmitted and inform design of novel therapies for rare diseases, like AGS.