A 2171-bp SacI/SacII DNA restriction fragment encompassing the 3' end of exon 5 through the 5' end of exon 7 was replaced by an internal ribosomal entry site (IRES) followed by the coding sequence for humanized Renilla green fluorescent protein (hrGFP) and a loxP-flanked neomycin resistance (PGK1-neo) cassette. RT-PCR using primers within the deleted sequence detect no transcript in homozygous mutant lung; using primers from a non-deleted region reveals only trace amounts of mRNA. Absence of the endogenous protein was confirmed by immunohistochemistry of mutant lung tissue. No hrGFP protein is detected by fluorescence confocal microscopy, immunoblot or immuhohistochemical analysis using antibodies to hrGFP. (J:122736)