Covalent Modification of p73α by SUMO-1

Two-hybrid screening in yeast with p73α isolated SUMO-1 ( s mall u biquitin-like mo difier 1 ), the enzyme responsible for its conjugation, Ubc-9, and a number of novel SUMO-1-interacting proteins, including thymine DNA glycosylase, PM-Scl75, PIASx, PKY, and CHD3/ZFH. A subset of these proteins contain a common motif, hhX S X S/T aaa , where h is a hydrophobic amino acid and a is an acidic amino acid, that is shown to interact with SUMO-1 in the two-hybrid system. We show here that p73α, but not p73β, can be covalently modified by SUMO-1. The major SUMO-1-modified residue in p73α is the C-terminal lysine (Lys 627 ). The sequence surrounding this lysine conforms to a consensus SUMO-1 modification site b ( X ) XXh K X E, where b is a basic amino acid. SUMO-1-modified p73 is more rapidly degraded by the proteasome than unmodified p73, although SUMO-1 modification is not required for p73 degradation. SUMO-1 modification does not affect the transcriptional activity of p73α on an RGC-luciferase reporter gene in SK-N-AS cells. Instead, SUMO-1 modification may alter the subcellular localization of p73, because SUMO-1-modified p73 is preferentially found in detergent-insoluble fractions. Alternatively, it may modulate the interaction of p73 with other proteins that are substrates for SUMO-1 modification or which interact with SUMO-1, such as those identified here.