nls b42 hagt where v5 stands for v5 epitope nls for sv40 large t antigen nuclear localization sequence and b42 stands for an artificial transcriptional activator b42 ma et al 1987 the last codon of the b42 transactivation domain is followed by the 21 amino acid sequence askkgtelgsttsngrqcagil the last three codons include a eco ri site for the c terminal cloning of the hagt to b42 a not i site is the c terminal restriction site for the hagt whose sequence includes a stop codon ii hagt ha ura3 where ura3 stands for the yeast enzyme orotic acid decarboxylase and ha stands for the ha epitope here the stop codon for the hagt is replaced by rs linker followed by the first amino acid of the ha tag the ha tag is directly followed by the ura3 gene iii hagt dhfr ha where dhfr stands for the mouse dihydrofolate reductase and ha stands for the ha epitope construction see example b and iv ssn6 hagt where ssn6 stands for a yeast repressor of dna transcription schultz et al 1987 here the stop codon of hagt is replaced by codons for the amino acids rsgsg which are then followed by the codon for the first amino acid of ssn6 of yeast a methionine the expression of all genes.