Transcription factors of the nuclear factor (NF)-κB/Rel family translocate into the nucleus upon degradation of the IκBs. Postinduction repression of NF-κB activity depends on NF-κB–regulated resynthesis of IκBα, which dissociates NF-κB from DNA and exports it to the cytosol. We found that after activation, p65/RelA is degraded by the proteasome in the nucleus and in a DNA binding–dependent manner. If proteasome activity is blocked, NF-κB is not promptly removed from some target genes in spite of IκBα resynthesis and sustained transcription occurs. These results indicate that proteasomal degradation of p65/RelA does not merely regulate its stability and abundance, but also actively promotes transcriptional termination.