"Steric gate" in DNA polymerase catalytic domain plays an essential role for the selection of nucleotides

 An aromatic amino acid such as tyrosine in the catalytic domain of DNA polymerases composes a "steric gate" for selecting the incorporated nucleotide definitely. The steric gate topologically inhibits the optimal localization of ribonucleotide in the polymerase catalytic domain by interfering with the 2'-OH of ribonucleotide, which results in the specifically selection of deoxyribonucleotide as the substrate for enzyme. Therefore, DNA polymerases, which utilize deoxyribonucleotide as the substrate, possess the essential aromatic amino acid in its catalytic domain to form the steric gate.