Fig. 6. A truncated form of Sog binds to PS1 integrin. Co-immunoprecipitation of Sog with various anti-integrin antibodies. Protein lysates were prepared from wild-type pupae (24 hours apf) and then incubated with protein A-Sepharose bound anti-ßPS, anti-PS1 or anti-PS2 antibodies. Lysates (lys), unbound supernatants (unb) and bound (bd1 and bd2) protein samples were run on 10% SDS-PAGE, immunoblotted and detected by the polyclonal 8A anti-Sog antiserum, which recognizes an epitope following CR1. (A) The Sog antibody reacts strongly with a large 120 kDa fragment in pupal lysates. A smaller 50 kDa reactive fragment is also present at very low levels. After co-immunoprecipitation with anti-PS1, the 50 kDa band is greatly enriched and small amounts of the full-length band are detected (arrowhead). Sog protein does not coimmunoprecipitate with the anti-ßPS antibody, but does co-immunoprecipitate to a much lesser extent with PS2. No binding was observed for short or full-length Sog with the protein ASepharose beads alone. (B) The structure of Sog protein indicating the transmembrane domain (TM), four cysteine repeats (CR1-CR4) and putative Tolloid cleavage sites (arrows). The blue bar indicates the predicted fragment corresponding to the 50 kDa Sog band that co-immunoprecipitates with anti-PS1. The red bar indicates the location of the epitope recognized by the 8A anti-Sog antibody.

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