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N-trimer in purified preparations of recombinant hantaviral N protein
(produced in the baculovirus-driven system in insect cells). This was
not totally unexpected as the hantaviral N protein was previously
shown to form trimers. 16,17,19 Our reconstruction of the hantaviral
N-monomers showed a striking similarity to structures described in the
literature: (1) earlier, low-resolution single-particle reconstructions of
the N-protein complexes of rabies virus, 29 and (2) the most recent,
high-resolution crystallography data for RNA complexes of rabies and
vesicular stomatitis viruses. 13,14 For example, the twisted shape char-
acteristic for hantaviral N-monomers (Fig. 2) is apparent in the tightly
formed RNP of rabies virus (see the space-filling model on Fig. 3A in
Albertini et al. , 2006 13 ). A relatively thin link between N-terminal and
C-terminal domains in the nucleoproteins of rabies and vesicular
stomatitis viruses (see Fig. 1C in Albertini et al. , 2006 13 and Fig. 1B
in Green et al. , 2006 14 ) can be easily recognized in the hantaviral
N-trimer (Fig. 2C, tilted side view, marked with arrow).
Reconstruction of the N-trimer structure, together with the RNA
docking data, led to the hypothesis on the mechanism of RNA chap-
eroning by the hantaviral N-trimer. The main idea is that the vRNA
panhandle is dissociated by the trimer as a result of solving a steric
conflict presented by the fitting together of two highly specific 3D
structures formed by the interacting parties. Here it is important to
stress that single monomers cannot perform the task and it is a specific
structure, the N-trimer, which supposedly acts as a chaperone. It remains
to be seen whether N-oligomers of other NSRVs can act as RNA chap-
erones, and if so, what would be the underlying mechanism.
Striking similarities have been observed between RNP complexes
formed by the hantaviral N protein with non-specific RNA and cor-
responding structures described for the following other NSRVs:
influenza, vesicular stomatitis and rabies viruses. The ring-like struc-
tures formed by 10 to 12 N-monomers associated with RNA were most
noticeable. These findings suggest a common mechanism of forma-
tion and functioning of viral RNPs. It is also worth mentioning that,
in the higher-order RNP-structures, the hantaviral N-trimers are not
seen. This could be explained by the absence of virus-specific, pan-
handle-forming RNA sequences in the pool of encapsidated cellular
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