A conditional by inversion (COIN) intron consisting of a lox66_SA-HA tag-IRES-Egfp-rabbit beta-globin polyA_lox71 was inserted in the antisense orientation after AAG codon encoding lysine 2384 in exon 34 via homologous recombination. The two lox sites are in reverse complementation orientation, thus cre-mediated recombination will irreversibly invert the inserted sequence. In addition an FRT flanked UBp-neomycin selection cassette was inserted after the COIN intron. Flp-mediated recombination removed the neomycin cassette. Cre-mediated recombination inverted the inserted sequence resulting in the expression of an HA-tagged truncated protein lacking the PEST domain and Egfp.