Alignment of zebrafish truncated β1 sequences. The alignment was performed using ClustalW. Protein domains are annotated: PSI, plexin/semaphorin/integrin; EGF, epidermal growth factor. Yellow bar indicates the position of a putative flexible linker region in EGF-2 . Domain boundaries in the EGF repeats are as predicted by Takagi et al. . Based on this prediction, the truncated β1 sequences contain four additional residues after the end of EGF-4. The position of an additional cysteine residue in EGF-4 (not seen in other β subunits) is indicated by tial. Sequence identities are indicated by *, conservative substitutions by :, semi-conservative substitutions by.