An inducible enzyme is a part of the operon model, which illustrates a way for genes to turn "on" and "off". Although in general it is inductively formed by the enzyme substrate, other compounds exhibiting hyper induction of the enzyme can be obtained by mass-screening, where each of various compounds is added into the culture media of a microorganism. We have investigated microbial metabolism of nitrile compounds through the following two enzymatic pathways: nitrilase (NitA) hydrolyzing nitrile to acid and ammonia; and nitrile hydratase (NHase) hydrating nitrile to amide. We have discovered that an actinomycete, Rhodococcus rhodochrous J1 strain produces the both enzymes, depending on the corresponding inducer. NHase and NitA are inductively overexpressed (more than 35% of all soluble proteins) on the addition of amide and nitrile, respectively, to the culture media. R. rhodochrous J1 has been used for the industrial production of acrylamide and nicotinamide, respectively.
Streptomyces with the ability of producing biologically active compounds such as antibiotics is an industrially important genus. Using each of the transcriptional regulation mechanisms and the strong gene promoters of the both enzymes, we constructed hyper expression systems in Streptomyces. After modifying the restriction enzyme gene region, using each of the gene promoters , we also succeeded in the development of expression vectors in Rhodococcus, which belongs to actinomycetes and has recently been expected as a new generation host under unconventional bioprocess environments.