The N-end rule: functions, mysteries, uses.

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. Similar but distinct versions of the N-end rule operate in all organisms examined, from mammals to fungi and bacteria. In eukaryotes, the N-end rule pathway is a part of the ubiquitin system. I discuss the mechanisms and functions of this pathway, and consider its applications.