Recently, the authors sequencing the archaeon Caldiarchaeum unearthed a remarkable operon with the entire core of the ubiquitin system containing genes encoding Ubiquitin, E1,E2,E3 and the deubiquitinase of the JAB family(also called MPN1) (Click here to read). These proteins are remarkable in that they share several sequence features with their eukaryotic counterparts. Further, the archaeon, like all members of its clade, contains the archaeo-eukaryotic proteasomal degradation system, suggesting the presence of the basic complement of the ubiquitin-based protein turnover system.
Great progress has also been made on the biochemistry of the other peptide-tag based protein turnover system; the pupylation pathway. A large number of substrates have now been reported and we also know that the Pup-ligase (PafA) paralog (also called Dop) which in some species deamidates glutamine, is a depupylase (Click here to read).
The consequence of these studies raises some interesting possibilities and questions.
1. Do any species have the entire complement of both the ubiquitin and pupylation based protein turnover/tagging system?
2. If so, how is the labor of protein turnover divided between pupylation and ubiquitination?
3. In light of the discovery in Caldiarchaeum, what can we say about the origins of the Ub-system?
Answers to these questions are in the following post. Click here to access the answers.
