Summary auto-generated
This study investigates how herpes simplex virus type 1 (HSV-1) controls the incorporation of tegument proteins into virus particles. The tegument is a protein-rich structure underlying the viral envelope, containing approximately 15 virus-encoded polypeptides. The researchers created a mutant virus (vUL37IEP) where the UL37 gene promoter was replaced with a strong cytomegalovirus promoter, increasing UL37 protein expression approximately 20-fold in infected cells. Despite this dramatic increase in cellular UL37 protein abundance, Western blot analysis of purified virions and L-particles (non-infectious particles containing tegument and envelope but lacking the capsid) revealed no detectable increase in UL37 protein incorporation. This contrasts sharply with VP22, another tegument protein whose incorporation increases when its expression is elevated. The findings indicate that UL37 protein abundance in virus particles is tightly regulated by a specific control mechanism independent of cellular protein levels. Since UL37 is present equally in both virions and L-particles, the regulation does not depend on capsid interaction. The results suggest tegument assembly involves selective incorporation mechanisms that differ among tegument proteins.
Key findings
- Increasing UL37 protein expression 20-fold in infected cells does not increase its incorporation into HSV-1 virions or L-particles, indicating tight control of tegument composition
- Unlike VP22, the abundance of UL37 in virus particles is not directly proportional to its expression level in infected cells
- UL37 protein incorporation is controlled by a mechanism independent of capsid interaction, since UL37 levels are equal in both infectious virions and capsid-free L-particles
- The tegument assembly pathway exhibits selective protein incorporation mechanisms, with different tegument proteins subject to different regulatory controls
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Abstract
The tegument region of herpes simplex virus type 1 virus particles contains approximately 15 virus-encoded polypeptide species. One of the less abundant species is a 120 kDa protein specified by gene UL37. The abundance of the UL37 protein in infected cells was increased about 20- fold by replacing the native promoter for gene UL37 with the strong immediate early promoter of human cytomegalovirus. This rise in abundance did not induce any detectable increase in the amount of UL37 protein incorporated into virus particles. These data contrast with those previously obtained for a second tegument protein VP22 whose level of incorporation was elevated by increasing its abundance in infected cells. Thus, for the UL37 protein, a mechanism exists to control its abundance in the tegument. Moreover, data obtained with light particles which lack the viral capsid suggest that this controlled incorporation is not directed by interaction with the capsid structure.