Professor Jane Jackman, from the Department of Chemistry and Biochemistry at Ohio State University, will visit the IUP Chemistry Department on Friday, October 7, 2011, and present a lecture on tRNA guanylyltransferase.
Dr. Jackman will visit with department faculty and students before presenting the lecture “Putting it in reverse: 3'-5' nucleotide addition catalyzed by tRNAHis guanylyltransferase enzymes” from 3:35 to 4:25 p.m. in Weyandt 240. Light refreshments will be served, and all are welcome to attend.
The tRNAHis guanylyltransferase (Thg1) is an essential enzyme in yeast that catalyzes the addition of a single indispensable G residue (G-1) to the 5'-end of tRNAHis. Addition of G-1 occurs via an unusual 3'-5' nucleotide addition reaction, in the opposite direction to nucleotide addition catalyzed by all known DNA/RNA polymerases. Nonetheless, the recent crystal structure of human Thg1 revealed unexpected structural homology between Thg1 and canonical 5'-3' DNA polymerases, suggesting that Thg1 similarly uses a two metal-ion active site for nucleotide addition. The mechanism by which Thg1 uses this well-studied active site to catalyze reverse (3'-5') nucleotide addition is currently under investigation.
Thg1 is a member of a large enzyme family with members in eukarya, where G-1 addition is universally required, but Thg1-like proteins (TLPs) have been identified in archaea, bacteria, and mitochondria, where the biological function of the enzymes is less well-understood. Using biochemical and genetic techniques, we have identified roles for TLPs in previously unknown nucleic acid 5'-end repair and editing reactions, providing evidence for novel uses for Thg1-catalyzed 3'-5' nucleotide addition reactions in biology. These activities are likely to play critical roles in maintaining a high-quality pool of cellular RNAs.