INTERACTION OF MESSENGER-RNA WITH THE ESCHERICHIA-COLI RIBOSOME - ACCESSIBILITY OF PHOSPHOROTHIOATE-CONTAINING MESSENGER-RNA BOUND TO RIBOSOMES FOR IODINE CLEAVAGE
Ev. Alexeeva et al., INTERACTION OF MESSENGER-RNA WITH THE ESCHERICHIA-COLI RIBOSOME - ACCESSIBILITY OF PHOSPHOROTHIOATE-CONTAINING MESSENGER-RNA BOUND TO RIBOSOMES FOR IODINE CLEAVAGE, Nucleic acids research, 24(12), 1996, pp. 2228-2235
The contacts of phosphate groups in mRNAs with ribosomes were studied,
Two mRNAs were used: one mRNA contained in the middle two defined cod
ons to construct the pre- and the post-translocational states, the oth
er was a sequence around the initiation site of the natural cro-mRNA.
Phosphorothioate nucleotides were randomly incorporated at a few A, G,
U or C positions during in vitro transcription, iodine can cleave the
thioated positions if they are not shielded by ribosomal components,
Only a few minor differences In iodine cleavage of ribosome bound and
non-bound mRNA were observed: the nucleotide two positions upstream of
the decoding codons (i.e. those codons involved in codon-anticodon in
teractions) showed a reduced accessibility for iodine and the nucleoti
de immediately following the decoding codons an enhanced accessibility
in bath elongating states, in initiating ribosomes where the mRNA con
tained a strong Shine-Dalgarno sequence, at least five phosphates were
additionally slightly protected covering the Shine-Dalgarno sequence
and nucleotides down-stream including the initiator AUG in the P site
(A1, G3, G-2, G-5 and A-7), The low contact levels of the phosphates i
n the mRNA with the elongating ribosome strikingly contrast with the p
ronounced contact patterns previously described for tRNAs. The data ob
tained in this study, as well as results of previous studies, suggest
that mRNA regions downstream and upstream of decoding codons form only
weak contacts with ribosomal components and that the mRNA thus is mai
nly fixed by codon-anticodon interaction on the elongating ribosome.