FIG. 4.

Deletion of D2 diminishes but does not abolish RPTPα oligomerization. (A) A schematic of the D2 deletion mutant construct. (B) 293 cells transiently expressing ΔD2 protein were cross-linked or not cross-linked with BS³. Shown are the results of an immunoblotting analysis with anti-HA tag MAb 12CA5 on whole-cell lysates using ECL detection. (C) Transiently transfected 293 cells were biotinylated. Whole-cell lysates were immunoprecipitated with MAb 12CA5 to isolate the total RPTPα proteins, which were then subjected to SDS-PAGE and probed with ¹²⁵I-labeled streptavidin to determine the levels of surface-expressed RPTPα protein. (D) Transiently transfected 293 cells were cross-linked with BS³. Whole-cell lysates were subjected to immunoblotting analysis using MAb 12CA5 followed by ¹²⁵I-labeled sheep anti-mouse IgG F(ab′)₂ to determine the levels of RPTPα dimers. Biotinylation (C) and cross-linking (D) were done on parallel dishes from the same transfection. Shown in panels C and D are images obtained via PhosphorImager analysis. S/M, surface-expressed monomeric proteins.