Nucleic Acids Research, Vol 25, Issue 14 2835-2840, Copyright © 1997 by Oxford University Press
K Gowda and C Zwieb
Signal recognition particle (SRP) is a ribonucleoprotein complex that
associates with ribosomes to promote the co-translational translocation of
proteins across biological membranes. Human SRP RNA molecules exist in two
distinct conformations, SR-A and SR-B, which may exchange during the
assembly of the particle or could play a functional role in the SRP cycle.
We have used systematic site-directed mutagenesis of the SRP RNA to
determine the electrophoretic mobilities of altered RNA molecules, and we
have identified the nucleotides that avert the formation of the two
conformers. The conformer behavior of the various RNAs was addressed
quantitatively by calculating a value zeta as an indicator of
conformational variability. Single loose A-like forms were induced by
changes in helix 5 [nucleotides (nt) at positions 111-128 or 222-231],
helix 6 (nt at positions 141-150) and helix 7 (nt at position 169 and 170),
whereas other mutations in helix 6 and helix 8 preserved the conformational
variability of the mutant RNA molecules. The more compact B-like form was
induced only when a small region (129-CAAUAU- 134), located in the
5'-proximal portion of helix 6, was altered. Since this region is part of
the binding site for SRP19, we suggest that protein SRP19 uses nucleotides
at 129-134 to trigger the formation of the favored SR-B-form, and thus
directs an early step in the hierarchical assembly of the large SRP domain.
ARTICLES
Determinants of a protein-induced RNA switch in the large domain of signal recognition particle identified by systematic-site directed mutagenesis
Department of Molecular Biology, The University of Texas Health Science Center at Tyler, Highway 271 N, PO Box 2003, Tyler, TX 75710, USA.
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