Wild-type 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) (this encodes 128 amino acids that lie mostly within the non-conserved N-terminal part of Su(H)) followed by the wild-type Mmus\Rbpj coding region starting at position V81 in the Mmus\Rbpj sequence. As a result of the engineering event, a residual attR site is present in the first intron, and most of this intron is duplicated; correct splicing of this intron has been confirmed.