What is "threose nucleic acid"

n. (context biochemistry English) An analog of RNA in which the sugar component is threose—considered to be a primordial precursor to RNA

Threose nucleic acid (TNA) is an artificial genetic polymer invented by Albert Eschenmoser. TNA has a backbone structure composed of repeating threose sugars linked together by phosphodiester bonds. Like DNA and RNA, TNA can store genetic information in strings of nucleotide sequences ( G, A, C, and T). TNA is not known to occur naturally and is synthesized chemically in the laboratory under controlled conditions. It is believed by some that TNA could be an evolutionary pathway to RNA.

TNA has generated great interest in synthetic biology because TNA polymers are resistant to nuclease degradation. This property, coupled with its ability to undergo Darwinian evolution in a test-tube, provide a possible path to biologically stable molecules with relevance in material science and molecular medicine.

TNA can self-assemble by Watson-Crick base pairing into duplex structures that closely approximate the helical geometry of A-form RNA. TNA can also form base pairs complementary to strands of DNA and RNA, which makes it possible to share information with natural genetic polymers. This capability and chemical simplicity suggests that TNA could have preceded RNA as a genetic material.

Polymerases have been identified that can replicate TNA polymers in the laboratory. TNA replication occurs through a process that mimics RNA replication. In these systems, TNA is reverse transcribed into DNA, the DNA is amplified by the polymerase chain reaction and then forward transcribed back into TNA.

TNA replication coupled with in vitro selection has produced a TNA aptamer that binds to human thrombin. This example demonstrates that TNA is capable of heredity and evolution, which is a hallmark of life. TNA can fold into complex shapes which can bind to a desired target with high affinity and specificity. It may be possible to evolve TNA enzymes with functions required to sustain early life forms.