The outer surface of the archaebacterium Haloferax volcanii (formerly named Halobacterium volcanit) is covered with a hexagonally packed surface (S) layer. The gene coding for the S-layer protein was cloned and sequenced. The mature polypeptide is composed of 794 amino acids and is preceded by a typical signal sequence of 34 amino acid residues. A highly hydrophobic stretch of 20 amino acids at the C-terminal end probably serves as a transmembrane domain. Clusters of threonine residues are located adjacent to this membrane anchor. The S-layer protein is a glycoprotein containing both N-and 0-glycosidic bonds. Glucosyl-(l-*2)-galactose disaccharides are linked to threonine residues. The primary structure and the glycosylation pattern of the S-layer glycoproteins from Haloferax volcanii and from Halobacterium halobium were compared and found to exhibit distinct differences, despite the fact that three-dimensional reconstructions from electron micrographs revealed no structural differences at least to the 2.5-nm level attained so far (M. Kessel, I. Wildhaber, S. Cohe, and W. Baumeister, EMBO J. 7:1549EMBO J. 7: -1554EMBO J. 7: , 1988.

The sex‐inducing pheromone of Volvox carteri is a glycoprotein that triggers development of males and females at a concentration below 10(−16) M. Evidence is presented for the existence of a novel mechanism of signal amplification operating within the extracellular matrix of this multicellular organism. A family of 70 kDa matrix glycoproteins denoted pherophorins bear a C‐terminal domain being homologous to the sex‐inducing pheromone. Under the influence of the pheromone, this domain is liberated by highly specific proteolysis.