Site-directed mutagenesis converted cysteine codon 303 (TGT) in exon 12 to phenylalanine (TTT) (p.C303F). Additional, silent, mutations were introduced in the next two downstream codons to introduce a diagnostic SpeI restriction site. A loxP site flanked neomycin resistance gene cassette that was inserted into intron 10 was removed through subsequent Cre-mediated recombination. The mutation disrupts binding of the encoded peptide to Smr3a (RPL5) and RPL11 gene products. (J:164200)