Part of salm exon 1 has been deleted (including the ATG codon). It has been replaced by a cassette containing: 1. a strong splice acceptor followed by stop codons and an SV40 polyA terminator and 2: a Disc\RFPDsRed.3xP3.cUa marker. The inserted DNA is flanked by inverted attP sites (thus it can subsequently be replaced using recombinase-mediated cassette exchange).