A novel gene cluster including the Rhodococcus rhodochrous J1 nhlBA genes encoding a low molecular mass nitrile hydratase (L-NHase) induced by its reaction product.

The 3.5 kilobases (kb) of the 5'-upstream region from nhlBA encoding a cobalt-containing low molecular mass nitrile hydratase (L-NHase) from Rhodococcus rhodochrous J1 was found to be required for the amide-dependent expression of nhlBA in experiments using a Rhodococcus transformation system. Sequence analysis of the 3.5-kb fragment revealed the presence of two open reading frames (nhlD and nhlC) in this fragment. NhlD has similarity to regulators MerR, CadC, and ArsR. NhlC has similarity to the regulators AmiC, for the expression of an aliphatic amidase from Pseudomonas aeruginosa, and NhhC, for the expression of a high molecular mass nitrile hydratase from R. rhodochrous J1. Assays of NHase activity of transformants carrying nhlD deletion or nhlC deletion mutations suggest a negative regulatory role for nhlD and a positive regulatory role for nhlC in the process of the L-NHase formation. Assays of NHase and amidase activities and Western blot analyses of each Rhodococcus transformant carrying various deletion plasmids, have shown that nhlBA and amdA encoding an amidase, which is located 1.9 kb downstream of nhlBA, were regulated in the same manner. These findings present the genetic evidence for a novel gene cluster controlling the expression of L-NHase, which is induced by the reaction product (amide) in the "practical microorganism" R. rhodochrous J1.