In vitro selection is a technique used to isolate high-affinity, high-specificity single-stranded nucleic acid molecules. It typically consists of several steps: library construction, functional selection and selective amplification. However, natural nucleic acid (DNA and RNA) aptamers suffer from low biostability because they are easily degraded by nucleases in biological context. It is therefore desirable to apply the in vitro selection methodology to xeno-nucleic acids (XNAs), which contain chemically modified backbones and are resistant to nuclease-mediated degradation. In this process, two major challenges needs to be addressed: 1) chemical synthesis of XNA monomer building blocks; 2) polymerases that recognize and accept XNAs as substrates.
DNA is typically viewed as a chemically inert genetic material. However, laboratory evolution yielded single-stranded DNA and RNA molecules that can fold into distinct tertiray structure and are capable of catalyzing chemical reactions. And these catalytically active nucleic acid molecules are named DNAzymes (or deoxyribozymes) and ribozymes, respectively. We have isolated a DNAzyme sequence that could catalyze breakage of phosphoester bond in RNA, with help of metal ions in solution.
Commonly twenty amino acids are used during protein transltion, and a wide range of post-translation modifications (PTMs) such as methylation, acetylation and phosphorylation endow proteins with new properties and are important to regulate the activities. To study the role of a specific PTM, it often requires synthesis of proteins with this modification. The current technology uses native protein expression followed by enzymatic modification, or solid-phase synthesis of modified peptide and chemical conjugation to the rest of protein. Genetic code expansion is a technique that introduces a new pair of transfer RNA and synthetase, and incorporate unnatural amino acids directly in response to a specific codon.