Localization to the Nuclear Envelope and Transport of the Glycoprotein B of Herpes Simplex Virus Type 1

Abstract

<p>Herpes simplex virus type I (HSV-1), acquires its envelope by budding through a modified inner membrane of the nuclear envelope (NE) which forms thick and dense patches at the site of budding. This suggests that some of the viral envelope constituents, such as the transmembrane glycoprotein B (gB), are specifically transported to the NE in order to be incorporated into the virus. In this thesis, it is shown by immunoelectron microscopy that gB is specifically localized in the NE of HSV-1 infected cells. Glycoprotein B was distributed on the outer and inner membrane of the NE. The distribution was homogeneous and no preferential accumulation was detected around or within the patches where the viruses bud.</p> <p>To determine which segments specify NE localization of gB, the distribution by immunofluorescence and by immunoelectron microscopy of deletion mutants and chimeras were investigated by transient expression in COS cells. The rate of transport and the oligomeric nature of the mutants were also studied. The chimeras were constructed by fusing domains of gB with domains of glycoprotein G of vesicular stomatitis virus, a transmembrane protein which does not accumulate in the NE. When the ectodomain (EC) of G was replaced with the EC of gB, the resulting chimera did not accumulate in the NE. On the other hand, all the mutants containing a peptide of 75 residues that encompasses the TM of gB were localized to the NE, suggesting that the TM contains the NE localization determinants. However, this domain does not appear to be essential, because swapping the TM of gB for the TM of G did not abolish NE localization. Furthermore, gB and all the mutants that were localized to the NE were also present in the ER suggesting the presence of an ER localization signal as well.</p>