Furthermore, PID, SH2, and DAG are also connected domains. Most Shc-like PID domain (PFAM: PF00640) ligands are RTKs or cytokines. Phosphotyrosine-independent Dab-like PID domains appear to mediate alternative signaling pathways such as endocytosis/processing or exocytosis. The PTB domains are classified as phosphotyrosine-dependent IRS-like, phosphotyrosine-dependent Shc-like, and phosphotyrosine-independent Dab-like. Phosphotyrosine interaction domains are the names given to the final two PTBs (PID or PI domains).