dAT joining: please define
In the context of this book, dAT joining is a method used in molecular cloning to join two DNA molecules. Basically, terminal transferase is used to add polyA or polyT to the 3' ends of each DNA molecule. This creates cohesive ends which can anneal and then be ligated together, giving a covalently closed circular DNA molecule.



Image from: Jackson DA, Symons RH, Berg P. 1972. Biochemical Method for Inserting New Genetic Information into DNA of Simian Virus 40: Circular SV40 DNA Molecules Containing Lambda Phage Genes and the Galactose Operon of Escherichia coli. Proc Nat Acad Sci USA 69(10):2904-2909.

See also: Lobban PE, Kaiser AD. 1973. Enzymatic end-to-end joining of DNA molecules. J Mol Bio 78(3):453-460.



dAT joining can also refer to an assay of DNA ligase activity. Linear dAT oligomers are incubated with the ligase, which can circularize them and make them resistant to exonuclease digestion. This resistance to digestion correlates with DNA ligase activity. 

Modrich P, Lehman IR. 1970. Enzymatic Joining of Polynucleotides. J Biol Chem 245(14):3626-3631.