A coenzyme-F420 non-reducing [NiFe] hydrogenase was isolated from Methanococcus voltae. It consist of three subunits. They are the products of the prevously identified genes vhuA, vhuG and vhuU. The vhuU gene product is of only 25 amino acids. This novel very small hydrogenase subunit contains selenocysteine within a conserved amino-acid sequence previously shown to be involved in Ni coordination. The subunit is shorter than the predicted primary gene product and is therefore apparently post-translationally processed.