A ppk enhancer followed by the core promoter and 5' UTR of Hsp70 is fused upstream of the z second intron followed by sequences encoding the transmembrane domain of Hsap\CD4 followed by a tandem dimer composed of a copy of EGFP and a copy of GFP. An endoplasmic reticulum export signal from Hsap\KCNJ2 is fused to the C-terminus of the tandem dimer sequence. 3'UTR and polyA sequences from His2Av are present downstream of the coding region.