mRNA Cap Formation - Structure and Mechanism of Yeast RNA Triphosphatase

RNA triphosphatase is an essential mRNA processing enzyme that catalyzes the first step in mRNA cap formation. The RNA triphosphatases are not conserved among eukarya and fall into at least 2 mechanistically and structurally distinct families: 1) the divalent cation-dependent RNA triphosphatases of DNA viruses and fungi, and 2) the divalent cation-independent RNA triphosphatases of nematodes, mammals, and other metazoa.

DNA Damage Recognition and Repair by DNA Ligases

The genetic connections between DNA repair pathways and human cancer predisposition have fueled interest in the proteins that recognize and repair specific sites of DNA damage. The repair enzymes are remarkably conserved from bacteria to fungi to humans, underscoring the premium placed on maintaining genomic integrity in the face of a mutagenic burden.

Topoisomerase I Structure and Mechanism

Type IB eukaryotic DNA topoisomerases modulate the topological state of DNA by cleaving and rejoining one strand of the DNA duplex. Cleavage is a transesterification reaction in which the scissile NpN phosphodiester is attacked by a tyrosine of the enzyme, resulting in the formation of a DNA-(3’-phosphotyrosyl)-enzyme intermediate and the expulsion of a 5’-OH polynucleotide.