Abstract
BackgroundHerpes simplex virus type 1 (HSV-1) has a complicated life-cycle, and its genome encodes many components that can modify the cellular environment to facilitate efficient viral replication. The protein UL14 is likely involved in viral maturation and egress (Cunningham C. et al), and it facilitates the nuclear translocation of viral capsids and the tegument protein VP16 during the immediate-early phase of infection (Yamauchi Y. et al, 2008). UL14 of herpes simplex virus type 2 exhibits multiple functions (Yamauchi Y. et al, 2001, 2002, 2003).MethodsTo better understand the function(s) of UL14, we generated VP16-GFP-incorporated UL14-mutant viruses with either single (K51M) or triple (R60A, R64A, E68D) amino acid substitutions in the heat shock protein (HSP)-like sequence of UL14. We observed the morphology of cells infected with UL14-null virus and amino acid-substituted UL14-mutant viruses at different time points after infection.ResultsUL14(3P)-VP16GFP and UL14D-VP16GFP (UL14-null) viruses caused similar defects with respect to growth kinetics, compartmentalization of tegument proteins, and cellular morphology in the late phase. Both the UL14D-VP16GFP and UL14(3P)-VP16GFP viruses led to the formation of an aggresome that incorporated some tegument proteins but did not include nuclear-egressed viral capsids.ConclusionsOur findings suggest that a cluster of charged residues within the HSP-like sequence of UL14 is important for the molecular chaperone-like functions of UL14, and this activity is required for the acquisition of functionality of VP16 and UL46. In addition, UL14 likely contributes to maintaining cellular homeostasis following infection, including cytoskeletal organization. However, direct interactions between UL14 and VP16, UL46, or other cellular or viral proteins remain unclear.
Highlights
Herpes simplex virus type 1 (HSV-1) has a complicated life-cycle, and its genome encodes many components that can modify the cellular environment to facilitate efficient viral replication
We previously showed that the UL14 protein of HSV type 2 (HSV-2) facilitates the translocation of both capsid protein VP26 and UL33 protein into the nucleus in cells co-expressing these proteins in the absence of viral infection[7]
K51 is conserved in both a-herpes viruses and the sequence 60RLKSRARLE68 of UL14, which contains a cluster of charged residues, and this region is highly similar to Hsp70 [6,9]
Summary
Herpes simplex virus type 1 (HSV-1) has a complicated life-cycle, and its genome encodes many components that can modify the cellular environment to facilitate efficient viral replication. UL14 of herpes simplex virus type 2 exhibits multiple functions (Yamauchi Y. et al, 2001, 2002, 2003). Herpes simplex virus (HSV) type 1 (HSV-1) is a large, enveloped DNA virus whose genome contains at least 74 genes [1,2]. We previously showed that the UL14 protein of HSV type 2 (HSV-2) facilitates the translocation of both capsid protein VP26 (which is encoded by the UL35 gene) and UL33 protein into the nucleus in cells co-expressing these proteins in the absence of viral infection[7]. Upon infection, UL14 is incorporated into the virion as a minor tegument protein, and it is required for efficient growth of the virus [5,6]
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