Fig. 3. Sog cleavage by Tld is modulated by Tsg. (A) The indicated combinations of proteins were incubated for 4 hours at 25°C, and Sog fragments were analyzed using an anti-Sog-CR1 antibody or anti-myc antibody. Tld requires Dpp to cleave Sog. In this experiment, the Dpp concentration was 10^-9 M. The molecular weight of each fragment was calculated relative to markers as: 110 kDa for a, 80 kDa for b, 65 kDa for c, 110 kDa for d, 65 kDa for e, 50 kDa for f and 33 kDa for g. (B) Sog is cleaved in at least five sites. The site marked with an asterisk is cleaved during secretion and was identified to be between R⁷⁹-H⁸⁰ by protein sequencing. This removes the type II transmembrane domain. The sites I, II, III and IV were cleaved by Tld in a Dpp-dependent fashion. Processing at the C-terminal site IV to produce fragment g was greatly enhanced in the presence of Tsg.

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