THE HELC GENE ENCODES A PUTATIVE DEAD-BOX RNA HELICASE REQUIRED FOR DEVELOPMENT IN DICTYOSTELIUM-DISCOIDEUM

DEAD-box RNA helicases, defined by the sequence Asp-Glu-Ala-Asp (DEAD, in single-letter amino-acid code), regulate RNA unwinding and seconda ry structure in an ATP dependent manner in vitro [1] and control mRNA stability and protein translation. Both yeast and mammals have large f amilies of DEAD box proteins, many of unknown function. We have disrup ted a Dictyostelium discoideum gene, helC, which encodes helicase C, a member of the DEAD-box family of RNA helicases that shows strong homo logy to the product of the essential Saccharomyces cerevisiae gene dbp 5 [2] and to related helicases in mouse and Schizosaccharomyces pombe. The HelC protein also shows weaker homology to the translation initia tion factor elF-4a. Other DEAD-box-containing proteins, which are less closely related to HelC, have been implicated in developmental roles in Drosophila [3] and Xenopus laevis; one example is the Xenopus Vasa like protein (XVLP) [4-6]. In Drosophila and Xenopus, Vasa and XVLP, r espectively, are required for the establishment of tissue polarity dur ing development. In yeast, DEAD-box helicases such as Prp8 [7] are com ponents of the spliceosome and connect pre-mRNA splicing with the cell cycle. Disruption of the helC gene in D. discoideum led to developmen tal asynchrony, failure to differentiate and aberrant morphogenesis. W e postulate that one reason for the existence of large families of hom ologous DEAD-box proteins in yeast, mammals and Dictyostelium could be that some DEAD-box proteins have developmentally specific roles regul ating protein translation or mRNA stability. (C) Current Biology Ltd I SSN 0960-9822.