Nucleoprotein (NP) binds to the viral RNA genomic segments in a
sequence-independent manner to form ribonucleoprotein complexes and
protect the viral genome from degradation. The protein contains
nuclear localization signals to allow for the import of the viral
genome into the host nucleus. Due to its size, NP is not
translocated into the nucleus. Although NP lacks enzymatic
activity, it is also involved in transcription as an elongation
factor for viral RNA polymerase and viral replication through
recruitment to ribonucleoprotein complexes. Interactions with
polymerase basic proteins 1 and 2 have been demonstrated. During
later stages of infection, NP is involved in viral packaging.
Matrix protein 1 (M1) may interact with NP to hide the nuclear
localization signal and thus allow the formation of viral
particles. Upon a new infection, M1 dissociates from NP due to the
acidification of the viral particle caused by matrix protein 2
(proton channel).
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