Localizing Function

More evidence that shows the importance of location for cellular function:

Like doctors making house calls, some DNA repair enzymes can relocate to the part of the cell that needs their help, a collaborative team of scientists at Emory University School of Medicine has found.


One DNA repair enzyme they studied, Ntg1, moves to the nucleus or the mitochondria depending on where DNA damage is concentrated, the authors found. In contrast, a related enzyme, Ntg2, stays in the nucleus under all conditions.

Cells appear to direct Ntg1’s relocation by briefly attaching a small protein called SUMO to what needs to be moved around, the authors found. SUMO is found in fungi, plants and animals and is already being investigated by several research groups as a possible target for anti-cancer drugs.

DNA repair mechanisms relocate in response to stress

Ah, yes. SUMO.

SUMO stands Small Ubiquitin-related MOdifier and a whole new “conceptually similar” story surrounds this little fella. Ubiquitin (Ub) is an exceptionally well conserved, eukaryotic-specific protein (mentioned in the DM) that tags other proteins for destruction. For ubiquitin to work, it depends on a 3-component accessory system (E1E2E3) that recognizes misfolded or unwanted proteins and attaches Ub to them.

SUMO likewise is attached to a variety of proteins, using a very similar accessory system, except that when it is added, it helps localize proteins. Like Ub, SUMO is attached to a lysine residue on the substrate protein. And what’s most cool is that SUMO, while having essentially the same structure as Ub, has a very different amino acid sequence.

Oh, and SUMO is not only found “in fungi, plants and animals,” it is found among all the various unicellular eukaryotic cells.

But this is all another story for another day.

3 responses to “Localizing Function

  1. And what’s most cool is that SUMO, while having essentially the same structure as Ub, has a very different amino acid sequence.

    So SUMO and Ub are not homologous?

  2. Who knows? Conventional thinking would say they are homologous because of their great structural similarity and other similarities in the way they are processed.

  3. I thought conventional thinking said that for two proteins to be homologous, they must share a certain percentage of amino acids.

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