Inventions disclosed herein relates to vectors and expression systems for producing heteromeric recombinant proteins such as monoclonal antibodies. Vectors and expression systems disclosed herein are based on the finding that the selectable marker glutamine synthetase can be divided into two fragments at selected amino acid positions of the glutamine synthetase polypeptide, and the two fragments can internet and/or associate to form a monomer and then a functional multimeric glutamine synthetase protein. Z

Described are compositions and methods for treating or preventing cancer in a subject by administering a pharmaceutical composition comprising a strain of Mycobacteria including an expression vector of the present invention into the bladder of a subject. The pharmaceutical composition may be administered by any suitable means including by a catheter.

One or more genes in a biosynthesis pathway for a vitamin or other essential nutrient which is needed for the survival of a microorganism can be used as an effective selective marker to identify cells transformed with an exogenous nucleic acid. The microorganism does not naturally contain or express the one or more gene. This permits genetic manipulations to be performed. It permits lower cost fermentations to be performed. It permits production of the essential nutrient for subsequent commodity use.

One or more genes in a biosynthesis pathway for a vitamin or other essential nutrient which is needed for the survival of a microorganism can be used as an effective selective marker to identify cells transformed with an exogenous nucleic acid. The microorganism does not naturally contain or express the one or more gene. This permits genetic manipulations to be performed. It permits lower cost fermentations to be performed. It permits production of the essential nutrient for subsequent commodity use.

Inventions disclosed herein relates to vectors and expression systems for producing heteromeric recombinant proteins such as monoclonal antibodies. Vectors and expression systems disclosed herein are based on the finding that the selectable marker glutamine synthetase can be divided into two fragments at selected amino acid positions of the glutamine synthetase polypeptide, and the two fragments can internet and/or associate to form a monomer and then a functional multimeric glutamine synthetase protein.