Search

Herpesviruses must cross the inner nuclear membrane and underlying lamina to exit the nucleus. HSV-1 US3 and PKC can phosphorylate lamins and induce their dispersion but do not elicit all of the phosphorylated lamin species produced during infection. UL13 is a serine threonine protein kinase conserved among many herpesviruses. HSV-1 UL13 phosphorylates US3 and thereby controls UL31 and UL34 nuclear rim localization, indicating a role in nuclear egress. Here, we report that HSV-2 UL13 alone induced conformational changes in lamins A and C and redistributed lamin B1 from the nuclear rim to intranuclear granular structures. HSV-2 UL13 directly phosphorylated lamins A, C, and B1 in vitro, and the lamin A1 tail domain. HSV-2 infection recapitulated the lamin alterations seen upon expression of UL13 alone, and other alterations were also observed, indicating that additional viral and/or cellular proteins cooperate with UL13 to alter lamins during HSV-2 infection to allow nuclear egress.

The UL13 protein kinase is conserved among many herpesviruses but HSV-2 UL13 specificity is not known. Here, we found that HSV-2 UL13 is a phosphoprotein that autophosphorylates, and that serines within ERK and Cdc2 motifs were important for autophosphorylation but not for UL13 phosphorylation of exogenous substrates. HSV-2 UL13 phosphorylated a peptide also recognized by ERK and Cdc2. However, mutation of substrate residues critical for Cdc2 or Erk phosphorylation did not alter HSV-2 UL13 phosphorylation of the peptide, and HSV-2 UL13 did not phosphorylate standard Cdc2 or Erk peptide substrates. Mutation of prolines surrounding the peptide phosphoacceptor site reduced phosphorylation by HSV-2 UL13, and a peptide containing serine-proline amid alanines and glycines was phosphorylated. Thus, HSV-2 UL13 does not mimic ERK or Cdc2 substrate recognition and its minimal recognition motif can be serine-proline. This motif's simplicity indicates that distal sequence or protein structure contributes to HSV-2 UL13 substrate specificity.