Abstract: Recombinant DNA sequences which encode the complete amino acid sequence of a glutamine synthetase, vectors containing such sequences and methods for their use, in particular as dominant selectable markers, for use in co-amplification of non-selected genes and in transforming host cell lines to glutamine independence.

Abstract: Recombinant DNA sequences which encode the complete amino acid sequence of a glutamine synthetase, vectors containing such sequences, and methods for their use, in particular as dominant selectable markers, for use in co-amplification of non-selected genes and in transforming host cell lines to glutamine independence are disclosed.

Abstract: There is described a method for obtaining a eukaryotic cell containing in its DNA multiple copies of a GS gene, comprising: transforming a eukaryotic glutamine auxotroph with a GS gene; selecting transformant cells containing the GS gene; and culturing the selected transformant cells in a medium which lacks glutamine or in which the amount of glutamine is progressively depleted, the GS gene being of a character such that, or the conditions employed during the culturing step being such that, the GS gene is so weakly transcribed that the cells in which the GS gene has been amplified are selected.

Abstract: The invention provides expression vectors containing the promoter, enhancer and substantially complete 5'-untranslated region including the first intron of the major immediate early gene of human cytomegalovirus. Further vectors including the hCMV-MIE DNA linked directly to the coding sequence of a heterologous gene are described. Host cells transfected with the vectors and a process for producing heterologous polypeptides using the vectors and the use of the hCMV-MIE DNA for expression of a heterologous gene are also included within the invention.