Stable Expression of Three Genes from a Tricistronic Retroviral Vector Containing a Picornavirus and 9-nt Cellular Internal Ribosome Entry Site Elements

Retroviral vectors are used widely to deliver heterologous genes into cells. In order to express three genes from a single RNA molecule, a retroviral vector that contains two divergent internal ribosome entry site (IRES) sequences has been constructed successfully. To eliminate the high frequency of recombination within a mulicistronic retrovirus vector, a 9-nt segment of a cellular mRNA IRES and a picornaviral IRES were used, since these two IRES sequences have minimal sequence homology. After a single round of replication, most cells infected with this vector stably expressed the three genes while approximately 40% of cells infected with another tricistronic retroviral vector that contains two copies of an identical IRES sequence lost expression of the gene located between these two sequences.