Methylation of the ribosyl moiety at position 34 of selenocysteine tRNA[Ser]Sec is governed by both primary and tertiary structure
The selenocysteine (Sec) tRNA[Ser]Sec population in higher vertebrates consists of two major isoacceptors that differ from each other by a single nucleoside modification in the wobble position of the anticodon (position 34). One isoacceptor contains 5-methylcarboxymethyluridine (mcmU) in this positi...
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Veröffentlicht in: | RNA (Cambridge) 2000-09, Vol.6 (9), p.1306-1315, Article S1355838200000388 |
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Zusammenfassung: | The selenocysteine (Sec) tRNA[Ser]Sec
population in higher vertebrates consists of two major isoacceptors
that differ from each other by a single nucleoside modification in the
wobble position of the anticodon (position 34). One isoacceptor contains
5-methylcarboxymethyluridine (mcmU) in this position, whereas the other
contains 5-methylcarboxymethyluridine-2′-O-methylribose
(mcmUm). The other modifications in these tRNAs are
N6-isopentenyladenosine
(i6A), pseudouridine (ψ), and 1-methyladenosine
(m1A) at positions 37, 55, and 58, respectively.
As methylation of the ribose at position 34 is influenced
by the intracellular selenium status and the presence of
this methyl group dramatically alters tertiary structure,
we investigated the effect of the modifications at other
positions as well as tertiary structure on its formation.
Mutations were introduced within a synthetic gene encoded
in an expression vector, transcripts generated and microinjected
into Xenopus oocytes, and the resulting tRNA products
analyzed for the presence of modified bases. The results
suggest that efficient methylation of mcmU to yield mcmUm
requires the prior formation of each modified base and
an intact tertiary structure, whereas formation of modified
bases at other positions, including mcmU, is not as stringently
connected to precise primary and tertiary structure. These
results, along with the observations that methylation of
mcmU is enhanced in the presence of selenium and that this
methyl group affects tertiary structure, further suggest
that the mcmUm isoacceptor must have a role in selenoprotein
synthesis different from that of the mcmU isoacceptor. |
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ISSN: | 1355-8382 1469-9001 |
DOI: | 10.1017/S1355838200000388 |