Xenopus c-ski contains a novel coiled-coil protein domain, and is maternally expressed during development

v-ski is a virally transduced nuclear oncogene. The biology of its cellular progenitors is only poorly understood. The early development of Xenopus laevis provides an excellent model system for studying the role of genes in proliferation, differentiation and development. We have therefore characterized Xenopus c-ski. We report that Xenopus c-ski transcripts are maternally regulated during early development, and are widely expressed in adult tissues. Structural predictions indicate the presence of a previously unreported extensive C-terminal helical domain in Xenopus c-ski and ski-related proteins from other species. This domain shows homologies with proteins which contain heptad repeats characteristic of elongated coiled-coil formation, like myosin and the intermediate filament proteins, and itself has a heptad repeat structure. The ski C-terminal domain also contains two other previously unreported elements, a novel strictly alternating hydrophobic-basic motif that repeats along the helical domain, and an underlying 25-mer repeated sequence. The significance of these findings is discussed with reference to c-ski function and to the oncogenic activation of v-ski, which is a truncated version of c-ski and thus does not have the C-terminal helical domain.