AP site

An AP site is a site in the DNA, which contains neither purines nor pyrimidines, mostly due to DNA damage or a DNA glycosylase. The abbreviation stands for apurinic or apyrimidinic AP site. If an AP site remains unrepaired, it can lead to a mutation during replication of DNA because doing a random base is inserting in the opposite strand. Many polymerases adenine is preferentially incorporated (A -rule ).

AP sites are often repaired by AP endonucleases. These remove any or several nucleotides on the 5 'side of the AP site and add new nucleotides using the undamaged complementary strand as a template a. If only one nucleotide is to repair, a so-called " short-chain Repair" ( engl. "short patch repair" ) is applied mechanism, among others, the DNA ligase II is used. If more than one nucleotide needs to be replaced, then a so-called " long chain repair " (English " long patch " ) is used mechanism, in which case the DNA ligase I, along with several other factors fills the gap again.