Orphan nuclear bodies.

Orphan nuclear bodies are defined as nonchromatin nuclear compartments that have been less well studied compared with other well-characterized structures in the nucleus. Nuclear bodies have traditionally been thought of as uniform distinct entities depending on the protein "markers" they contain. However, it is becoming increasingly apparent that nuclear bodies enriched in different sets of transcriptional regulators share a link to the ubiquitin-proteasome and SUMO-conjugation pathways. An emerging concept is that some orphan nuclear bodies might act as sites of protein modification by SUMO and/or proteasomal degradation of ubiquitin-tagged proteins. By defining a specialized environment for protein modification and degradation, orphan nuclear bodies may increase the capacity of cells to survive under varying environmental conditions.