Abstract.The shelter of the tube-dwelling polychaete Sabellaria alveolata is composed of mineral particles as sembled with spots of a proteinaceous cement. The adhesive proteins constituting the cement were identified on the basis of their sequence similarity with proteins of a phylogenetically related species, Phragmatopoma californica. Two positively charged proteins, Sa-1 and Sa-2, share coimnon features: they both have a mass of 22 kDa; are rich in glycine, tyrosine and basic residues; and show repeated peptide motifs. The consensus repeat of Sa-1 is KGAY-GAKGLGYGNKAGYGAYG (occurring 6 -8 tunes), while Sa-2 displays the consensus heptapeptide VHKAAWG (5 tunes) and undecapeptide VHKAAGYGGYG (8 times). Two variants of a serine-rich protein, Sa-3A (22 kDa) and Sa-3B (21 kDa), were also identified. Their serine residues account for 75 mol% and are probably phosphorylated, meaning that Sa-3 is very acidic and negatively charged. Moreover, tyrosine residues of all adhesive proteins are presumably modified into DOPA. Although protein se quences are not well-conserved between S. alveolata and P. californica, their main characteristics (including amino acid composition, post-translational modifications, repeated pat terns, isoelectric point, and mass) are shared by both spe cies. This suggests that these features are more important for their function than the primary structure of the proteins. The mRNA abundance for each protein was esthnated by quan titative real-thne PCR, revealing relative expression levels