Proliferation and differentiation of T and B lymphocytes during an immune response are mediated by signaling that leads to phosphorylation of a protein called IKB. Unphosphorylated IKB binds to and inhibits the transcription factor NF-KB. Phosphorylated IKB releases NF-KB and is then ubiquitinated and degraded by a proteasome.
(a) Explain why this mechanism for activating NF-KB allows rapid changes in gene expression.
(b) Explain why directly phosphorylating NF-KB might not be an effective mechanism for altering gene expression.
(c) A protein produced by Yersinia pestis (the bacterium that causes plague) removes the ubiquitin molecules from IKB. How would this affect the immune response to the Yersinia infection?