Nucleic Acids Research, Vol 24, Issue 14 2648-2651, Copyright © 1996 by Oxford University Press
SI Kim, M Nalaskowska, JE Germond, D Pridmore and D Soll
In many organisms (e.g., gram-positive eubacteria) Gin-tRNA is not formed
by direct glutaminylation of tRNAGln but by a specific transamidation of
Glu-tRNAGln. We wondered whether a similar transamidation pathway also
operates in the formation of Asn-tRNA in these organisms. Therefore we
tested in S-100 preparations of Lactobacillus bulgaricus, a gram-positive
eubacterium, for the conversion by an amidotransferase of [14C]Asp-tRNA to
[14C]Asn-tRNA. As no transamidation was observed, we searched for genes for
asparaginyl- tRNA synthetase (AsnRS). Two DNA fragments (from different
locations of the L.bulgaricus chromosome) were found each containing an ORF
whose sequence resembled that of the Escherichia coli asnS gene. The
derived amino acid sequences of the two ORFs (432 amino acids) were the
same and 41% identical with E.coli AsnRS. When one of the ORFs was
expressed in E.coli, it complemented the temperature sensitivity of an
E.coli asnS mutant. S-100 preparations of this transformant showed
increased charging of unfractionated L.bulgaricus tRNA with asparagine.
Deletion of the 3'-terminal region of the L.bulgaricus AsnRS gene led to
loss of its complementation and aminoacylation properties. This indicates
that L.bulgaricus contains a functional AsnRS. Thus, the transamidation
pathway operates only for Gin-tRNAGln formation in this organism, and
possibly in all gram-positive eubacteria.
ARTICLES
Asn-tRNA in Lactobacillus bulgaricus is formed by asparaginylation of tRNA and not by transamidation of Asp-tRNA
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA.
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