Stable DNA constructs

摘要

Methods are provided for producing protein products in host cells and for selecting transformed cells comprising the step of transforming the host cell with a DNA molecule comprising a gene which complements a deficiency in the host cell. The host cell is s strain having a deficiency in a function necessary for normal cell growth. The gene in the DNA molecule, such as a plasmid, which complements the deficiency serves as a selection marker whereby the growth conditions for selection may comprise a conventional complex medium.