Expression vector, methods for the production of heterologous gene products, and selection method for high-producing recombinant cells

Disclosed is an expression vector for eukaryotic cells comprising a gene that codes for a protein of interest in a functional bond with a hamster ubiquitin/S27a promoter, and a gene which codes for a fluorescent protein. Preferably, the expression vector also comprises an amplifiable selection marker gene. Also disclosed are host cells, preferably mammal cells, which are transfected with the expression vector, methods for producing heterologous gene products, and a method for selecting high-producing cells.