RNA Recognition via the SAM Domain of Smaug

mRNA leads to improper accumulation of Nos in the2 Howard Hughes Medical Institute Department of Molecular Genetics & Microbiology bulk cytoplasm and defects in head development. For repression, the TCE contains a pair of redundant hair-Box 3657 Duke University Medical Center pins, each bearing the loop sequence CUGGC. Smg was identified in embryonic extracts as a 120 kDa factorDurham, North Carolina 27710 capable of binding wild-type TCE (Smibert et al., 1996). Subsequent studies of embryos lacking normal smg function and in vitro translation experiments demon-Summary strated that Smg is indeed required for repression of nos mRNA (Dahanukar et al., 1999; Smibert et al., 1999).The Nanos protein gradient in Drosophila, required for proper abdominal segmentation, is generated in part Although Smg is a large protein (999 amino acids), a domain consisting of residues 583–763 is sufficient tovia translational repression of its mRNA by Smaug. We report here the crystal structure of the Smaug RNA recognize the TCE hairpins (Dahanukar et al., 1999). Surprisingly, this RNA binding domain (RBD) shows nobinding domain, which shows no sequence homology to any previously characterized RNA binding motif. sequence homology to previously characterized RN