Complex formation between proteins encoded by the ski gene family

The c-ski proto-oncogene product (c-Ski) is localized in the nuclei, but its function and biochemical properties are unclear. C-Ski can bind to DNA only in association with uncharacterized protein(s). A lambda gt11 cDNA library was screened with the biotinylated Ski to isolate genes encoding proteins capable of forming complexes with Ski. Two clones encoding Ski itself or the ski-related gene product SnoN were isolated in this manner, suggesting that Ski can form a complex with Ski itself or with SnoN. Trimerization of Ski with itself and SnoN was also confirmed by protein cross-linking and protein blot analysis. The carboxyl-terminal 1/5 regions of Ski and SnoN are required for complex formation. This region has a homology between two proteins and two putative leucine zipper-like structures, suggesting that these leucine zipper-like structures mediate trimerization by making side-to-side interactions between the conserved leucines. Thus, Ski and SnoN have the capacity to associate with other proteins, and a complex formation of c-Ski with itself, SnoN, and uncharacterized proteins might play a key role in the function of Ski.