However, so far no sequence information from these macromolecules has been obtained. To date, the molecular mechanisms of underwater adhesion have been studied in most detail in animals, particularly the marine mussel Mytulis edulis. Mussels attach to surfaces via macroscopic fibers that contain tyrosine-rich proteins at their sticky end. In many mussel foot proteins tyrosine residues have been post-translationally hydroxylated to 3,4-dihydroxyphenyl-L-alanine. The presence of Dopa seems to play an important role in both structural integrity of the filaments and underwater adhesion to surfaces by forming covalent cross-links and coordination bonds with metal ions, as well as by forming hydrogen bonds with the surface. Also the adhesive proteins of other organisms, like polycheates, invertebrates, turbellarians, hydroids and tunicats contain significant amounts of Dopa. The pivotal role of Dopa-rich proteins in underwater surface adhesion of lower animals has prompted the question as to whether diatoms employ similar proteins. This question has been addressed in the present work using a bioinformatics-based approach. Amphora coffeaeformis was chosen for these studies, because it is one of the most common biofouling diatoms, and it has been used in many studies as a model organism for underwater bioadhesion. Previously, A. coffeaeformis had not been investigated on a molecular level, and thus neither genome nor transcriptome data were available for this species at the onset of this study. Through the present work we have made A. coffeaeformis amenable for investigations on the molecular mechanism of underwater adhesion through establishing a transcriptome database and a method for its molecular genetic transformation. These tools have then been employed to identify A. coffeaeformis proteins with similarities to mussel adhesion proteins, and first steps have been taken towards their functional characterization. The screening parameters were based on proteins that mediate underwater adhesion in marine mussels, which are highly enriched in both lysine and tyrosine residues. AC3362 contains two lysineand tyrosine-rich domains, but does not exhibit sequence similarity to mussel adhesion proteins. Studies on the functional characterization of AC3362 relied on a genetic transformation system for A. coffeaeformis that has also been established in the present study. This enabled the expression of an AC3362-YFP fusion protein and investigation of its location by fluorescence microscopy using both direct imaging of the YFP fusion protein and indirect immunolabeling with anti-YFP antibodies. The data clearly indicate that AC3362 is not a component of the adhesive material that is Compound Library secreted by the diatom cell. Instead, AC3362 is part of an insoluble organic matrix associated with the biosilica of the cell wall, similar to the cingulincontaining microrings recently described from T. pseudonana.