Date Published: February 11, 2016
Publisher: Public Library of Science
Author(s): Guoli Shi, Tomomi Ando, Ryosuke Suzuki, Mami Matsuda, Kenji Nakashima, Masahiko Ito, Tsutomu Omatsu, Mami Oba, Hideharu Ochiai, Takanobu Kato, Tetsuya Mizutani, Tatsuya Sawasaki, Takaji Wakita, Tetsuro Suzuki, Aleem Siddiqui.
Although information regarding morphogenesis of the hepatitis C virus (HCV) is accumulating, the mechanism(s) by which the HCV genome encapsidated remains unknown. In the present study, in cell cultures producing HCV, the molecular ratios of 3’ end- to 5’ end-regions of the viral RNA population in the culture medium were markedly higher than those in the cells, and the ratio was highest in the virion-rich fraction. The interaction of the 3’ untranslated region (UTR) with Core in vitro was stronger than that of the interaction of other stable RNA structure elements across the HCV genome. A foreign gene flanked by the 3’ UTR was encapsidated by supplying both viral NS3-NS5B proteins and Core-NS2 in trans. Mutations within the conserved stem-loops of the 3’ UTR were observed to dramatically diminish packaging efficiency, suggesting that the conserved apical motifs of the 3´ X region are important for HCV genome packaging. This study provides evidence of selective packaging of the HCV genome into viral particles and identified that the 3’ UTR acts as a cis-acting element for encapsidation.
It is known that positive strand RNA viruses package their genome via replication-coupled processes [1–3]. Nevertheless, for several viruses, viral particle assembly occurs via recognition of particular sequences or structures termed packaging signals that are unique to the viral genes. These signals are more conserved than other parts of the viral genomes and are usually highly structured. However, thus far, a packaging signal has not been identified for any member of the Flaviviridae family.
Evidence regarding the virion assembly of HCV has accumulated over the past years; however, the detailed mechanisms responsible for incorporation of viral genomes into progeny virions remain largely unclear.