Two systems for the co-expression of proteins in Escherichia coli were designed and constructed. The first system relies on the new vector, pGOOD, which is compatible with ColE1-type plasmids and sustains efficient co-expression of soluble protein complexes. The second system is based on the pGOOD1 vector (a derivative of pGOOD), useful for the production of toxic proteins, whose synthesis can be regulated by the co-expressed LacI repressor.