Acts as an E3 ubiquitin-protein ligase, which accepts ubiquitin from specific E2 ubiquitin-conjugating enzymes, and then transfers it to substrates promoting their degradation by the proteasome. Up-regulates STATc tyrosine phosphorylation via an inhibitory effect on ptpC accumulation. Recognizes activated receptor tyrosine kinases, RTKs and terminates signaling. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. A very small proportion appears to be nuclear but this may reflect cytoplasmic contamination of the nuclei. Expressed in the slug stages (at protein level). Expressed at a relatively low level in growing cells. Accumulates during the first few hours of development, to reach a plateau during aggregation. The RING-type zinc finger domain mediates binding to an E2 ubiquitin-conjugating enzyme. The N-terminus is composed of the phosphotyrosine binding (PTB) domain, a short linker region and the RING-type zinc finger. The PTB domain, which is also called TKB (tyrosine kinase binding) domain, is composed of three different subdomains: a four-helix bundle (4H), a calcium-binding EF hand and a divergent SH2 domain. Ubiquitinated. Migrating slugs frequently fragment and the basal disk of the culminants that are formed are absent or much reduced. The gene for this protein is duplicated in strains AX3 and AX4. These strains contain a duplication of a segment of 750 kb of chromosome 2 compared to the corresponding sequence in strain AX2.