A lacZ gene was inserted in frame within exon 1 followed by a PGK-neomycin resistance gene. This replaced sequence from 356bp to 724bp downsteam of the initiator codon for the "B" isoform. As a result, the coding sequence for a 122aa fragment was removed including the initiation codon for the "A" isoform. Care was taken not to disrupt the estrogen response elements. (J:79968)