The Rel/NF-kappa B transcription factors represent the paradigm? of re
gulation of transcriptional activation through subcellular localizatio
n. In unstimulated cells, NF-kappa B exists in an inactive state in th
e cytoplasm complexed to the inhibitory I kappa B molecules. Upon stim
ulation, I kappa B is rapidly degraded, freeing NF-kappa B to transloc
ate to the nucleus and to activate the expression, of its target genes
. In this chapter, we will summarize what is known about the structure
of I kappa B molecules, their functions, the mechanisms of I kappa B
degradation, and the most common upstream signaling pathway (that is,
serine phosphorylation) that leads to I kappa B degradation. Finally,
we will discuss alternative mechanisms for induction of NF-kappa B thr
ough regulation of I kappa B activity. (C) 1997 Academic Press Ltd.