Divergent Evolution of Nuclear Localization Signal Sequences in Herpesvirus Terminase Subunits

Valproic acid (VPA) is a small fatty acid used for treatment of different neurologic diseases such as epilepsy, migraines or bipolar disorders. In addition, N-terminally truncated cytoplasmic isoforms of LANA, resulting from internal translation initiation, have been reported, but their function is unknown. Here we report two high-quality capsid structures, from human herpes simplex virus type 1 (HSV-1) and the animal pseudorabies virus (PRV), imaged inside intact virions at ~7-Å resolution. These findings extend the roles of a γ-herpesvirus latent protein into the lytic replication cycle. In addition, stable viral producer cell lines based on iSLK cells have been created for wildtype KSHV, for 12 individual miRNA knock-out mutants (ΔmiR-K12-1 through -12), and for mutants deleted for 10 of 12 (ΔmiR-cluster) or all 12 miRNAs (ΔmiR-all). NMR heteronuclear single quantum correlation (HSQC) analysis revealed chemical perturbations after titration of USP7-NTD with vIRF1 (44)SPGEGPSGTG(53) peptide. All authors reviewed the results and approved the final version of the manuscript.

The tripartite terminase complex of herperviruses assembles in the cytoplasm of infected cells and exploits the host nuclear import machinery to gain access to the nucleus, where capsid assembly and genome-packaging occur. Similarly, SUMO-interacting motifs (SIMs) mediate the recognition of SUMOylation and enables SUMO modifications to serve as a platform to recruit additional proteins. We found a monopartite NLS at the N-terminus of large terminase, flanking the ATPase domain, that is conserved only in α-herpesviruses. In contrast, small terminase exposes a classical NLS at the far C-terminus of its helical structure, which is conserved only in two genera of the β-subfamily and absent in α- and γ-herpesviruses. In addition, we predicted a classical NLS in the third terminase subunit that is partially conserved among herpesviruses. In the present study, we demonstrate for the first time that upon KSHV infection the endogenous Hrs localizes to the plasma membrane and the membrane associated Hrs facilitates assembly of signaling molecules, macropinocytosis and virus entry. We propose that swapping NLSs among terminase subunits is a regulatory mechanism that allows different herpesviruses to regulate the kinetics of terminase nuclear import, reflecting a mechanism of virus:host adaptation.