A minigene construct contained intron 1 of the rabbit beta-globin sequence followed by an EGFP/cre fusion gene with a nuclear localization signal and a translational stop codon. Homologous recombination in ES cells replaced exon 1 and 3.6 kb of intron 1 of the Lrp2 locus with the EGFP/cre minigene. (J:181474)