p62, a phosphotyrosine-independent ligand of the SH2 domain of p56lck, belongs to a new class of ubiquitin-binding proteins.

Division of Tumor Virology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
Journal of Biological Chemistry (Impact Factor: 4.6). 09/1996; 271(34):20235-7. DOI: 10.1074/jbc.271.34.20235
Source: PubMed

ABSTRACT p62 is a novel cellular protein which was initially identified as a phosphotyrosine-independent ligand of the SH2 domain of p56(lck). In the yeast two-hybrid system, p62 specifically interacted with ubiquitin in vivo. Furthermore, p62 bound to ubiquitin-conjugated Sepharose beads in vitro and was efficiently competed by soluble ubiquitin. The interaction was independent of ATP hydrolysis, and its dissociation did not require a reducing agent. Thus, p62 binds to ubiquitin noncovalently. Further analysis showed that the C-terminal 80 amino acids of p62 were indispensable for its interaction with ubiquitin. However, p62 has homology neither with ubiquitin C-terminal hydrolases nor with the S5a subunit of the 26 S proteasome complex, the only proteins known to bind to ubiquitin noncovalently. These results suggest that p62 belongs to a new class of ubiquitin-binding proteins and that p62 affects signal transduction at least partly through ubiquitination-mediated protein degradation.

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