The mago nashi locus encodes an essential product required for germ plasm assembly in Drosophila.

In Drosophila, the localization of maternal determinants to the posterior pole of the oocyte is required for abdominal segmentation and germ cell formation. These processes are disrupted by maternal effect mutations in ten genes that constitute the posterior group. Here, the molecular analysis of one posterior group gene, mago nashi, is presented. Restriction fragment length polymorphisms and transcript alterations associated with mago nashi mutations were used to identify the mago nashi locus within a chromosomal walk. The mago nashi locus was sequenced and found to encode a 147 amino acid protein with no similarity to proteins of known or suspected function. The identification of the mago nashi locus was confirmed by sequencing mutant alleles and by P element-mediated transformation. Nonsense mutations in mago nashi, as well as a deletion of the 5' coding sequences, result in zygotic lethality. The original mago nashi allele disrupts the localization of oskar mRNA and staufen protein to the posterior pole of the oocyte during oogenesis; anterior localization of bicoid mRNA is unaffected by the mutation. These results demonstrate that mago nashi encodes an essential product necessary for the localization of germ plasm components to the posterior pole of the oocyte.