Smibert, C.A., Wilson, J.E., Kerr, K. and Macdonald, P.M. (1996).
smaug protein represses translation of unlocalized nanos mRNA in the Drosophila embryo.
Genes & Development 10, 2600-2609.
Abstract
nanos mRNA,
which encodes the localized component of the Drosophila posterior
body patterning determinant, is normally translated only at the posterior
pole of the embryo, where the mRNA is
concentrated. Here we identify two similar cis-acting
sequences in the nanos mRNA 3' untranslated region that
mediate translational repression. These sequences bind an embryonic protein
of 135 kD, smaug, and we refer to them as smaug recognition elements (SREs).
Analysis of point mutations in the SREs reveals a strong correlation between
smaug binding and translational repression; mutants unable to bind smaug
in vitro are not repressed translationally in vivo, whereas mutants that
do bind smaug remain repressed translationally. These results strongly suggest
that smaug acts in translational repression of unlocalized nanos mRNA.
Translational repression
is essential, as embryos expressing a nanos mRNA with mutated
SREs develop with anterior body patterning defects and die,
despite correct localization of the RNA.