Biology Reference
In-Depth Information
Fig. 2.
Three-dimensional structure of the MS2 packaging signal RNA
(1DOU).
viral replicase gene; however, biochemical studies showed that neither
of these is involved in direct interactions with the coat protein.
6
The
structure of the isolated RNA stem-loop has been determined by
NMR spectroscopy for a closely related virus, the bacteriophage R17.
7
The structure shows that the unpaired nucleotide (A-10, Fig. 2) is
intercalated in the stem. The entire segment of the sequence from G-
11 to C-3 shows signs of a high degree of flexibility. The position of
the bases in the loop is not very well defined. This type of partially
unstructured or highly dynamic RNA binding site is a feature found
in several RNA protein complexes.
8-11
The Coat Protein
The 129 amino acids comprising MS2 coat protein form dimers at
concentrations below 1.0
M. At higher concentrations these dimers
associate to form empty protein shells that are very similar in struc-
ture to native virus particles.
5,12
Each of these particles contains 90
coat protein dimers. Each monomer of the coat protein contains
seven
µ
β
-strands and two
α
-helices. Five of the
β
-strands are arranged
