UASt regulatory sequences are fused upstream of the E2f1-RA isoform 5'UTR, the sfGFP coding sequence and the longer (1265bp) E2f1 3'UTR. The 5'UTR sequence has been mutated so that single nucleotide substitutions (ATG to AAG) remove all 11 start codons of the upstream open reading frame (uORF) present in the 5'UTR.