(Ai) Western blot showing Tld-HA input proteins and the amount bound to GST-VkgNC1 in a pulldown experiment. (Aii) Graph shows the level of binding to Collagen IV plotted relative to binding of full-length Tld, based on data from three experiments. Error bars are SEM, n = 3, *p < 0.05. (B) Western blot (anti-HA) showing Tld input and the levels bound to Sog in the presence of Dpp, with or without (±) added Collagen IV. (Ci) Western blot (anti-Myc) of Sog cleavage by full-length Tld or the ΔCUB2 mutant quantified in (Cii). The x-axis labels (–,+,++) refer to the absence, or increasing amounts, of Tsg. Error bars are SEM, n = 3. (Di) Western blot (anti-Myc) of Tld cleavage of SogCR14*, with cleavage levels quantified in (Dii). Both cleavage assays were carried out over 3 hr, in the presence of Dpp, and in the absence or presence of increasing amounts of Tsg, with or without of Collagen IV, as indicated. Graphs show the fold-change in the relative levels of the 50 kDa and 33 kDa cleavage fragments released by Tld (green) or ΔCUB2 (blue), in the presence of Collagen IV relative to its absence. See also Figure 4—figure supplement 1.