Abstract: The invention relates to the construction and use of novel expression systems that make use of DNA sequences encoding a promoter or promoters along with cis-regulatory elements, such as those for proU, that permit osmotically inducible initiation of transcription in bacteria; the expression systems of the present invention can be used to efficiently hyperexpress heterologous gene products including proteins or polypeptides; methods for construction of vectors and strains enabling NaCl-induced hyperexpression of heterologous gene products in several organisms such as Escherichia coli, and methods for NaCl-induced hyperexpression of heterologous gene products, including proteins or polypeptides, using the said novel combinations in a variety of organisms such as Escherichia coli, and further purification of the gene product of interest in either laboratory or industrial scale production systems.