Abstract: The present invention provides compositions and method for regulating cellular growth and metabolism, intra- and extracellular enzymatic activities, and synthesis of endogenous and/or heterologous proteins, comprising the steps of cloning genes encoding an mRNA interferase (toxin) and its cognate antitoxin; expressing these proteins in a host cell from two separate constitutive or inducible promoters on one or more plasmid vectors or on a chromosome; and regulating the cellular growth and metabolism by controlling the ratio of toxin and antitoxin present in the host cell. Optionally, the method provides further steps of modifying an endogenous or heterologous gene of interest to substitute all mRNA recognition sequences with sequences that are not cleavable by the mRNA interferase being expressed without any change in the amino acid sequence of the protein encoded by the gene; and co-expressing the gene of interest in the same host cell.