Metallothioneins are low molecular-weight, cysteine-rich, trace metal-binding proteins. Whereas class III metallothioneins (MTs) have been isolated in eukaryotic algae, Anacystis nidulans (Synechococcus TX20) remains the only prokaryote in which a class II MT has been isolated and characterized. Cadmium binding ligands produced in response to cadmium were separated using gel permeation HPLC, DEAE and a variety of physical methods. Results indicated that, in addition to the class II MT previously isolated, putative class III (gammaEC)(_n)G polypeptides may have been induced by the cadmium ions. An attempt was made to isolate and characterize the first prokaryotic metallothionein gene. Two synthetic oligonucleotides analogous to the Synechococcus TX20 MT protein were used as extension primers in an attempt to amplify the MT gene locus
