Molecular Basis for Nuclear Egress of Herpesviruses

• Applicant: Professor Dr. Thomas C. Mettenleiter
• Subject Area: Virology
• Term: from 2012 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 226088690

Herpesvirus nucleocapsids are translocated from their assembly site in the nucleus to the cytosol by acquisition of a primary envelope at the inner nuclear membrane which subsequently fuses with the outer nuclear membrane. This vesicular transport of cargo through the nuclear envelope is novel in cell biology. It requires the presence of homologs of the conserved herpesviral pUL31 and pUL34 proteins which form the nuclear egress complex (NEC). The NEC recruits viral and cellular kinases to locally dissolve the nuclear lamina allowing access of nucleocapsids to the inner nuclear membrane and interaction with the NEC, which then drives primary envelopment by oligomerization of the NEC around the nucleocapsid. However, it is still unclear how cargo is recruited to the vesicle, how their fission occurs and, in particular, what drives their fusion with the outer nuclear membrane processes which may include not only viral but also cellular proteins. While in the first period we focussed on the elucidation of function and structure of the alphaherpesvirus NEC, we now want to continue by analysis of its oligomerization leading to vesicle formation probing for interacting surfaces predicted by the cryo-EM reconstruction; its activity in cargo (nucleocapsid) recognition by mutation of predicted NEC-capsid interacting sites; identify potential cellular proteins involved in fusion by CRISPR/Cas9 mutagenesis including as control virus mutants which leave the nucleus by nuclear envelope breakdown independent of the NEC which had been isolated in the first period by reversion analysis; and screen for structural and functional homologs of the NEC in the Alloherpesviridae which do not show significant sequence conservation but conservation of the nuclear egress pathway. These studies should not only shed more light on the molecular basis of herpesvirus nuclear egress but also identify cellular proteins involved in this unique vesicular nucleo-cytoplasmic transport.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Barbara Klupp