A loxP flanked PGK-neomycin selection cassette and an HA-tagged Stk39 cDNA containing two mutations, a threonine to glutamate change at residue 243 (T243E) and a serine to aspartate change at 383 (S383D), and an in-frame stop codon were inserted after the start codon of Stk39. Cre-mediated recombination excised the selection cassette resulting in expression of the constitutively active kinase under the control of the native gene promoter. (J:287773)