DNA sequence containing a pros-RJ cDNA with a deletion of sequence encoding amino acid residues 812-870, along with 2039bp of sequence upstream of the pros-RJ ATG start codon (including pros intron, promoter and 5'UTR) and 3265bp pros 3'UTR, and with the coding sequence tagged with Tag:MYC, has been introduced into the attP site present in TI{TI}prosKO.