A loxP site was inserted upstream of exon 2 and an FRT flanked neo cassette, loxP site and mutant exon 2 with a T377C mutation resulting in a C116R substitution were inserted downstream of exon 2 via homologous recombination. Cre mediated recombination removed exon 2 and the neo cassette. The mutation in exon 2 is in the first zinc finger and abrogates binding to RNA in in vitro assays. Expression levels of the mutant protein are similar to wild-type expression levels. (J:261625)