Determinants of pole cells, which are precursors of the germ line, are provided maternally and are localized to the posterior pole of the Drosophila egg, as are polar granules. It has been hypothesized that certain RNA molecules associated with polar granules may be necessary for pole cell determination. Using a monoclonal antibody (Mab46F11) against polar granules, we have cloned the gene for one of their components. This gene turns out to be vasa, which is required maternally for the formation of polar granules and germ cells. This polar granule component shows significant sequence similarity to eIF-4A, a translation initiation factor that binds to mRNA, and to other helicases.