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J. Virol., Dec 1995, 7461-7471, Vol 69, No. 12
E Santolini, L Pacini, C Fipaldini, G Migliaccio and N Monica
The NS2 protein of hepatitis C virus (HCV) is released from its polyprotein
precursor by two proteolytic cleavages. The N terminus of this protein is
separated from the E2/p7 polypeptide by a cleavage thought to be mediated
by signal peptidase, whereas the NS2-3 junction located at the C terminus
is processed by a viral protease. To characterize the biogenesis of NS2
encoded by the BK strain of HCV, we have defined the minimal region of the
polyprotein required for efficient cleavage at the NS2-3 site and analyzed
the interaction of the mature polypeptide with the membrane of the
endoplasmic reticulum (ER). We have observed that although cleavage can
occur in vitro in the absence of microsomal membranes, synthesis of the
polyprotein precursor in the presence of membranes greatly increases
processing at this site. Furthermore, we show that the membrane dependency
for efficient in vitro processing varies among different HCV strains and
that host proteins located on the ER membrane, and in particular the signal
recognition particle receptor, are required to sustain efficient
proteolysis. By means of sedimentation analysis, protease protection assay,
and site-directed mutagenesis, we also demonstrate that the NS2 protein
derived from processing at the NS2-3 site is a transmembrane polypeptide,
with the C terminus translocated in the lumen of the ER and the N terminus
located in the cytosol.
Copyright © 1995, American Society for Microbiology
The NS2 protein of hepatitis C virus is a transmembrane polypeptide
Istituto di Ricerche di Biologia Molecolare, Angeletti, Pomezia, Italy.
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