NF-KAPPA-B P105 PROCESSING VIA THE UBIQUITIN-PROTEASOME PATHWAY

The p50 subunit of NF-KB is generated by proteolytic processing of a 1 05-kDa precursor (p105) in yeast and mammalian cells. Here we show tha t yeast mutants in the ubiquitin-proteasome pathway inhibit or abolish p105 processing, Specifically, p105 processing is inhibited by a muta tion in a 20 S proteasome subunit (pre1-1), by mutations in the ATPase s located in the 19 S regulatory complexes of the proteasome (yta1, yt a2/sug1, yta5, cim5), and by a mutation in a proteasome-associated iso peptidase (deal). A ubiquitinated intermediate of the p105 processing reaction accumulates in some of these mutants, strongly suggesting tha t ubiquitination is required for processing. However, none of the ubiq uitin conjugating enzyme mutants tested (ubc1, -2, -3, -4/5, -6/7, -8, -9, -10, -11) had an effect on p105 processing, suggesting that more than one of these enzymes is sufficient for p105 processing. Interesti ngly, a mutant ''N-end rule'' ligase does not adversely affect p105 pr ocessing, showing that the N-end rule pathway is not involved in degra ding the C-terminal region of p105. Unexpectedly, we found that a glyc ine-rich region of p105 that is required for p105 processing in mammal ian cells is not required for processing in yeast. Thus, p105 processi ng in both yeast and mammalian cells requires the ubiquitin-proteasome pathway, but the mechanisms of processing, while similar, are not ide ntical.