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Cell. 1998 Mar 20;92(6):819-28.

Cotranslational biogenesis of NF-kappaB p50 by the 26S proteasome.

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Gladstone Institute of Virology and Immunology, Department of Microbiology and Immunology, University of California, San Francisco 94141, USA.


The NFkappaB1 gene encodes two functionally distinct proteins termed p50 and p105. p50 corresponds to the N terminus of p105 and with p65 (RelA) forms the prototypical NF-kappaB transcription factor complex. In contrast, p105 functions as a Rel-specific inhibitor (IKB) and has been proposed to be the precursor of p50. Our studies now demonstrate that p50 is generated by a unique cotranslational processing event involving the 26S proteasome, whereas cotranslational folding of sequences near the C terminus of p50 abrogates proteasome processing and leads to p105 production. These results indicate that p105 is not the precursor of p50 and reveal a novel mechanism of gene regulation that ensures the balanced production and independent function of the p50 and p105 proteins.

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