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Journal of Bacteriology, November 2000, p. 6302-6307, Vol. 182, No. 22
Department of Molecular Biology, The Hebrew
University-Hadassah Medical School, Jerusalem 91120, Israel
Received 13 July 2000/Accepted 30 August 2000
The UGA codon, which usually acts as a stop codon, can also
direct the incorporation into a protein of the amino acid
selenocysteine. This UGA decoding process requires a
cis-acting mRNA element called the selenocysteine insertion
sequence (SECIS), which can form a stem-loop structure. In
Escherichia coli, selenocysteine incorporation requires
only the 17-nucleotide-long upper stem-loop structure of the
fdhF SECIS. This structure carries a bulged nucleotide U at position 17. Here we asked whether the single bulged nucleotide located in the upper stem-loop structure of the E. coli
fdhF SECIS is involved in the in vivo interaction with SelB.
We used a genetic approach, generating and characterizing
selB mutations that suppress mutations of the bulged
nucleotide in the SECIS. All the selB suppressor
mutations isolated were clustered in a region corresponding to 28 amino
acids in the SelB C-terminal subdomain 4b. These selB suppressor mutations were also found to suppress mutations in either
the loop or the upper stem of the E. coli SECIS. Thus, the E. coli SECIS upper stem-loop structure can be
considered a "single suppressible unit," suggesting that there is
some flexibility to the nature of the interaction between this element
and SelB.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Bulged Nucleotide in the Escherichia coli Minimal
Selenocysteine Insertion Sequence Participates in Interaction with
SelB: a Genetic Approach
*
Corresponding author. Mailing address: Department of
Molecular Biology, The Hebrew University-Hadassah Medical School,
Jerusalem 91120, Israel. Phone: 972-2-678-8250. Fax: 972-2-6784010. E-mail: hanita{at}cc.huji.ac.il.
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