O6-alkylguanine-DNA alkyltransferases for efficient labeling of fusion proteins

The present invention relates to methods of transferring a label from suitable substrates to O6-alkylguanine-DNA alkyltransferase (AGT) fusion proteins, to suitable fusion proteins, to suitable variants of AGT, and to novel labeled fusion proteins obtained. A protein of interest is incorporated into an AGT fusion protein, the AGT fusion protein is contacted with an AGT substrate carrying a label, and the AGT fusion protein is detected and/or manipulated using the label in a system designed for recognizing and/or handling the label. This allows the detection and/or manipulating of the fusion protein, both in vitro and in vivo, by attaching mols. to the fusion proteins that introduce a new phys. or chem. property to the fusion protein. Examples of such mols. are, among others, spectroscopic probes or radioactively labeled mols., affinity tags, mols. generating reactive or hydroxyl radicals, cross-linkers and lipid. AGT in fusion protein is a human variant wherein Asn157 is replaced by Gly and Ser159 by Glu, and the one wherein Gly160 is replaced by Ala or Trp. AGT in fusion protein is a human variant wherein Asn157 is replaced by Ser, Ser159 by His, and Gly160 by Asn. [on SciFinder (R)]