JBC, Vol. 251, Issue 21, 6730-6734, Nov, 1976
Aminoacyl-tRNA conformation. Information from steroid and oligonucleotide probes
D. J. Dvorak and C. Kidson
The conformations of aminoacyl- and deacylated tRNA Phe (yeast) have been
compared by using the steroid progesterone and the tetranucleotides U-C-C-C
and C-G-A-A as probes of transfer RNA ordered structure. U-C-C-C is
complementary to G18-G19-G20-A21 in the dihydrouridine loop and C-G-A-A is
complementary to T54-psi55-C56-G57 in the ribosylthymine loop. None of the
probes bound to deacylated tRNA Phe but all three bound to
phenylalanyl-tRNA Phe, with molar association constants of the order of
10(4) M-1. The oligonucleotide binding data imply that the tertiary
hydrogen bonds between G18 and psi55, G19 and C56, T54 and m1A58, and A21
and the ribose of U8 (Quigley, G. J., Wang, A. H. J., Seeman, N. C.,
Suddath, F. L., Rich, A., Sussman, J. L., and Kim, S. H., (1975) Proc.
Natl. Acad. Sci. U.S.A. 72, 4866-4870) are destabilized or broken on
aminoacylation, unmasking the sequence T-psi-C-G thought to be involved in
ribosome binding of aminoacyl-tRNA. The presumed progesterone binding site
is G18-G19-G20, which is part of the binding site for U-C-C-C. Competition
was not, however, observed between these two probes; model building has
shown that they could, theoretically, bind simultaneously. Since
progesterone bound to N-acetyl-Phe-tRNA Phe, the introduction of the
additional positive charge on aminoacylation is not sufficient per se to
explain the conformational change. The association of progesterone with
peptidyl-tRNA Phe was similar to that with aminoacyl-tRNA Phe, implying
that no further conformational change takes place in the region of the
steroid binding site on formation of a peptide bond.
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