intron border of the first vcp intron 206 represents the start methionine of the vcp gene 208 represents the beginning of the selection marker gene i e the beginning of the sh ble gene atg 210 represents an introduced artificial sequence tt 212 represents the right intron border of the first vcp intron 214 represents the stop codon of the selection marker gene taa 216 represents where polyadenylation occurs after the ccgccc sequence 218 represents c from fig1 a 1b which is the dna sequence downstream of the vcp gene fig3 shows an exemplary nucleotide sequence seq id no 2 wherein the sh ble gene of the pl90 vector was replaced with a gene conferring resistance against hygromycin b 302 represents a from fig1 a 1b which is the dna sequence in front of the vcp gene 304 represents the left intron border of the first vcp intron 306 represents the start methionine of the vcp gene 308 represents the beginning of the selection marker gene i e the beginning of the hygromycin b phosphotransferase gene atg 310 represents an introduced artificial sequence tt 312 represents the right intron border of the first vcp intron 314 represents the stop codon of the selection marker gene taa 316 represents where polyadenylation occurs after the ccgccc sequence 318 represents c from fig1 a 1b which is the dna sequence downstream of the vcp gene fig4 shows an exemplary nucleotide sequence seq id no 3 wherein the sh ble gene of the pl90 vector was replaced with a gene conferring resistance against blastocidin 402 represents a from fig1 a 1b.