The Drosophila embargoed gene is required for larval progression and encodes the functional homolog of Schizosaccharomyces CRM1

The CRM1 (Exportin 1) protein is a receptor for leucine-rich nuclear export signal sequences. We have molecularly characterized the Drosophila melanog aster embargoed (emb) gene and find that it encodes a product with 49 and 7 1% sequence identity to the fission yeast Schizosaccharomyces pombe and hum an CRM1 proteins, respectively. We show that expression of the emb cDNA is sufficient to suppress the growth phenotype of both conditional-lethal and null S. pombe crm1(-) mutant strains, suggesting that emb encodes the funct ional homologue of the S. pombe Crm1 protein. Through mutagenesis screens w e have recovered a series of recessive lethal emb mutations. There is a sub stantial maternal contribution of emb mRNA and animals hemizygous for our e mb alleles can develop to second instar larvae but persist at this stage an d consistently fail to undergo the molt to the third instar stage. We see a nuclear accumulation of endogenous actin in the intestinal epithelial cell s of the emb mutant larvae, consistent with a role for the emb gene product in nuclear export of actin protein.