Hybrid 3′ untranslated regions suitable for efficient protein expression in mammalian cells

The present invention describes the use of hybrid short 3′ untranslated (3′UTR) regions which are composed of two regions, one region from an 3′ untranslated region of a stable eukaryotic mRNA, and another region from the downstream end of an 3′ untranslated region of another eukaryotic mRNA that contains a polyadenylation (polyA) signal. The use of such hybrid regions allows for an efficient protein expression when used in conjunction with circular or linear expression DNA molecules. The present invention provides a recombinant DNA that is composed of a promoter, a protein coding region, and the hybrid 3′UTR in a continuous and directional orientation. The efficient expression systems of the invention are suitable for the economical and efficient production of therapeutic proteins and for use with both transient and stable expression systems.