Construction and expression of a metallothionein-beta-glucuronidase gene fusion.

A gene fusion consisting of the Chinese hamster metallothionein II and beta-glucuronidase coding regions was constructed. The fusion protein expressed in Escherichia coli retained cadmium-binding capacity and beta-glucuronidase activity. When expressed from the constitutive 35S promoter in transgenic tobacco, the levels of 109Cd accumulation in leaves were reduced to about 70% of those in untransformed control plants. Metallothionin-beta-glucuronidase did not sequester a significant proportion of the leaf 109Cd taken up through the roots in vitro and therefore a sink for Cd was not created.