A cDNA encoding PDGFbetaR was targeted into the Pdgfrb locus. This allele serves as a control for Pdgfrbtm5Sor. The cDNA was inserted in frame into a Sma1 site in the second coding exon. Western blot analysis indicated that expression of the targeted Pdgfr locus was disrupted and the introduced receptor was expressed. (J:67735)