We have established that the gene which we had previously identified as encoding the Methanococcus voltae P-type ATPase is, in fact, the structural gene for the M. voltae S-lager protein. This conclusion is based on a comparison of the N-terminal sequence of S-layer protein prepared by two independent methods with that derived from the nucleotide sequence of the cloned gene. This conclusion was further supported by immuno-cytochemical localization of the antigen directed against the antibodies used in the cloning experiments.