M{loxP.attP} represents a transgenic construct generated in vivo by P1cre recombinase-mediated excision of the loxP cassette in M{3xP3-RFP.attP}, removing the Disc\RFP3xP3.PB marker and leaving a single attP site and a single loxP site. The attP site present in this element contains a T-C transition at position 26 downstream of the TTG site. This mutation is outside of the attP 'core region' of 39bp (minimal attP length defined in PMID:10801973) and is also outside the 'footprint' region bound by phiC31:int integrase (PMID:11069650) and so is not expected to affect the function of the attP site.