REQUIREMENT FOR THE VASA RNA HELICASE IN GURKEN MESSENGER-RNA LOCALIZATION

Localization of specific mRNAs to distinct sites within the Drosophila oocyte is an early and key step in establishing the anterior-posterio r and dorsal-ventral axes. We describe a new function for the RNA heli case encoded by the ''posterior'' group gene vasa (vas) in control of localization of the mRNA encoded by the ''dorsal-ventral'' patterning gene gurken (grk). Two new ethyl methane sulfonate-induced, female ste rile alleles of vas have been isolated. In these mutants grk mRNA fail s to become localized properly and GRK protein is barely detectable. S urprisingly fs(1)K10, a recessive female sterile mutation that results in mislocalization of GRK mRNA to the anterior end of the oocyte, is epistatic to these vas alleles. This result demonstrates that GRK prot ein levels sufficient to dorsalize the egg chamber can accumulate in v as mutants, if fs(1)K10 is also mutant. Taken together these results s uggest that regulation of GRK mRNA localization normally occurs, direc tly or indirectly, through the VAS RNA-dependent RNA helicase and may suggest that accumulation of GRK protein normally depends on GRK mRNA localization. (C) 1998 Academic Press.