Ablation of the expression of the most abundant isoform, Rarbeta2, encoded by this locus was achieved in two steps. First, all of the in-frame start codons for the Rarbeta2 isoform were eliminated by site-specific mutagenesis of nucleotides 459 through 491. Second, a neomycin resistance gene was inserted into the first exon of the Rarbeta2 isoform, exon 4. RT-PCR and Western blot analysis, using isoform specific primers and antibodies, showed a lack of Rarbeta2 mRNA and protein, as well as normal levels of transcript and protein corresponding to the other isoforms. (J:21486)