question: What is the biological role of K-48 linked protein ubiquitination?
answer: The proteasome, which identifies and destroys unwanted proteins rapidly, plays a vital role in maintaining cellular protein homeostasis. Proteins that are destined for proteasome-mediated degradation are usually tagged with a chain of ubiquitin linked via lysine (K) 48 that targets them to the proteolytic machinery. K(48)-linked polyubiquitinated proteins are degraded by the proteasomes to elevate cellular levels of amino acids needed for intracellular proliferation. NF-κB and ubiquitylation initially became linked when it was recognised that lysine (K)48-linked ubiquitin chains are involved in the processing of NF-κB precursors and the degradation of inhibitor of kappa B (IκB) proteins.