Fig S1. Scanning electron micrograph (SEM) of opened distal thread. (A) The knobby coating and fibrous interior of the distal portion of a Mytilus galloprovincialis byssal thread. The longitudinal axis of the thread runs from left to right. The scale bar is 10 m. (B) A higher magnification of the same thread shows bundles of fibers that are approximately 100−200 nm. The scale bar is 1 m.

Fig S2. C-terminal thread matrix protein (TMP) sequence alignment. (A) Sequence F3T7 was amplified from the cDNA library using PCR with the degenerate primer described in the Materials and methods. A hybridization of the cDNA library screen using the F3T7 yielded a further two C-terminal variants. (B) 3′ UTR of all three clones.

Fig S3. Thread matrix protein (TMP)-1 variant alignments. Rapid amplification to cDNA ends (RACE) and RT-PCR yielded two variants of the TMP-1, a and b. The () indicates the putative signal peptide cleavage site. Conserved amino acids are designated with a (*). Only a partially sequenced clone of TMP-1b is shown. Periods (...) indicate non-sequenced regions. Sequences were aligned using T-COFFEE (available at www.ch.embnet.org/software/TCoffee.html.).

Fig S4. Thread matrix protein (TMP)-2 variant alignments. Rapid amplification to cDNA ends (RACE) and RT-PCR yielded eight N-terminal TMP-2 variants, a−h. The () indicates the putative signal peptide cleavage site. Conserved amino acids are designated with a (*). Periods (...) indicate non-sequenced regions. Inter-individual variation was observed at the N-terminus of the mature protein, designated (SG) and (SS). Variant names in red were found as both (SG) and (SS) variants in different individuals; however, the sequences are shown as (SG) variants. Variant names in blue were found only as (SS) variants. All (SS) variants were from the same individual mussel. Sequences were aligned using the program T-COFFEE (available at www.ch.embnet.org/software/TCoffee.html.).