The FRT cassette containing EGFP has been excised, allowing expression of the brk coding sequence under the control of its own regulatory sequence. There are 13 potential silencer elements (SEs) in the brk regulatory sequences (12 upstream of the coding sequence, one downstream); in this transgene, each of the SE sites except site 10 has been made non-functional by introducing five point mutations that completely abrogate binding of Mad, Med and shn proteins in vitro (numbering of sites is distal to proximal). A multi-tag cassette composed of 2xTag:FLAG, 3xTag:HA and Tag:StrepII is present at the C-terminal end of the brk coding sequence.