A 5.5 kb region containing exons 2-4 (encoding amino acids 19-105) was replaced with a neomycin resistance cassette via homologous recombination. Homozygous mutant animals lacked protein product as determined by Western blot analysis of retinal proteins. Mutant retinas failed to express the long form of G protein, beta 5 (GNB5-L), although normal amounts of its mRNA were still present; however, a normal protein level of the short form GNB5-S was detected in the retina and striatum of mutant mice.