UASt regulatory sequences drive expression of a bicistronic translational sensor that comprises the E2f1-RA isoform 5'UTR followed by sfGFP tagged with Tag:NLS(Unk) and the longer (1265bp) E2f1 3'UTR. A RFP(Unk) coding sequence has been inserted into the 5'UTR sequence at nucleotide position 414.