Sj. Klug et al., IN-VITRO AND IN-VIVO CHARACTERIZATION OF NOVEL MESSENGER-RNA MOTIFS THAT BIND SPECIAL ELONGATION-FACTOR SELB, Proceedings of the National Academy of Sciences of the United Statesof America, 94(13), 1997, pp. 6676-6681
The special elongation factor SelB of Escherichia coli promotes seleno
cysteine incorporation into formate dehydrogenases, This is thought to
be achieved through simultaneous binding to selenocysteyl-tRNA(Sec) a
nd, in the case of formate dehydrogenase H, to an fdhF mRNA hairpin st
ructure 3' adjacent to the UGA selenocysteine codon, By in vitro selec
tion, novel RNA sequences (''aptamers''), which can interact tightly a
nd specifically with SelB, were isolated from an RNA library, The libr
ary was comprised of mutagenized variants of the wild-type fdhF mRNA h
airpin, One-half of the selected sequences contained the apical stem-l
oop of the fdhF mRNA hairpin highly conserved, Some of the aptamers sh
owed deviations in the primary sequence within this region of the wild
-type fdhF hairpin motif while still binding with high affinity to Sel
B, Binding studies performed with truncated versions of SelB revealed
that aptamers binding to different sites on the protein have been sele
cted, To dissect SelB binding to the fdhF hairpin from the overall bio
logical function of this complex, four selected aptamers were analyzed
in vivo for UGA readthrough in a lacZ fusion construct, Among these,
one promoted UGA readthrough in vivo. Three of the aptamers, however,
were drastically reduced or unable to replace the fdhF mRNA hairpin in
vivo, despite the similar secondary structure and binding affinities
of these RNAs compared with the wild-type motif, This finding implies
functions of the fdhF hairpin that go beyond the mere tethering off se
lenocysteyl-tRNA(Sec) to the UGA codon.