A promoterless beta-galactosidase/neomycin gene fusion (beta-geo) was inserted in frame into the exon coding for the signal peptide. Southern blot analysis demonstrated that three tandem copies of the beta-geo gene were present in a concatamer. Northern blot analysis failed to detect a PDGFbetaR transcript in homozygous mutants. Western blot analysis of total protein failed to detect any immunoreactive PDGFbetaR in homozygous mutants. (J:20016)