Nucleotidyltransferase

Nucleotidyltransferases are transferase enzymes of phosphorus-containing groups, e.g., substituents of nucleotidylic acids or simply nucleoside monophosphates. The general reaction of transferring a nucleoside monophosphate moiety from A to B, can be written as:
 * A-P-N + B $$\rightleftharpoons$$ A + B-P-N

For example, in the case of polymerases, A is pyrophosphate and B is the nascent polynucleotide. They are classified under EC number 2.7.7 and they can be categorised into:
 * 1) Uridylyltransferases, which transfer uridylyl- groups
 * 2) Adenylyltransferases, which transfer adenylyl- groups
 * 3) Guanylyltransferases, which transfer guanylyl- groups
 * 4) Cytitidylyltransferases, which transfer cytidylyl- groups
 * 5) Thymidylyltransferases, which transfer thymidylyl- groups

Role in DNA repair mechanisms
Nucleotidyl transferase is a component of the repair pathway for single nucleotide base excision repair. This repair mechanism begins when a single nucleotide is recognized by DNA glycosylase as incorrectly matched or has been mutated in some way (UV light, chemical mutagen, etc.), and is removed. Later, a nucleotidyl tranferase is used to fill in the gap with the correct base, using the template strand as the reference.