Mutated sequence from the Mmus\Rbpj gene (Su(H) ortholog) has been reintroduced into the attP site present in TI{TI}Su(H)attP, resulting in a transcription unit in which endogenous Su(H) regulatory sequences drive expression of the first exon and intron of Su(H) followed by a mutated Mmus\Rbpj coding region that carries a S221D amino acid substitution (phosphomimetic mutation).