A BayGenomics gene trap vector (pGT1lxf) was inserted into intron 20 to create an in frame 5' fusion product with a lacZ cassette. The absence of the 250KDa protein was confirmed by western blot with an antibody recognizing the C-terminus end of Flnb. A beta-galactosidase assay confirmed expression of the lacZ fusion product. (J:120066)