The Exonuclease Activity of Herpes Simplex Virus 1 UL12 Is Required for Production of Viral DNA That Can Be Packaged To Produce Infectious Virus.

The herpes simplex virus (HSV) type I alkaline nuclease, UL12, has 5'-to-3' exonuclease activity and shares homology with nucleases from other members of the Herpesviridae family. We previously reported that a UL12-null virus exhibits a severe defect in viral growth. To determine whether the growth defect was a result of loss of nuclease activity or another function of UL12, we introduced an exonuclease-inactivating mutation into the viral genome. The recombinant virus, UL12 D340E (the D340E mutant), behaved identically to the null virus (AN-1) in virus yield experiments, exhibiting a 4-log decrease in the production of infectious virus. Furthermore, both viruses were severely defective in cell-to-cell spread and produced fewer DNA-containing capsids and more empty capsids than wild-type virus. In addition, DNA packaged by the viral mutants was aberrant, as determined by infectivity assays and pulsed-field gel electrophoresis. We conclude that UL12 exonuclease activity is essential for the production of viral DNA that can be packaged to produce infectious virus. This conclusion was bolstered by experiments showing that a series of natural and synthetic α-hydroxytropolones recently reported to inhibit HSV replication also inhibit the nuclease activity of UL12. Taken together, our results demonstrate that the exonuclease activity of UL12 is essential for the production of infectious virus and may be considered a target for development of antiviral agents.IMPORTANCE Herpes simplex virus is a major pathogen, and although nucleoside analogs such as acyclovir are highly effective in controlling HSV-1 or -2 infections in immunocompetent individuals, their use in immunocompromised patients is complicated by the development of resistance. Identification of additional proteins essential for viral replication is necessary to develop improved therapies. In this communication, we confirm that the exonuclease activity of UL12 is essential for viral replication through the analysis of a nuclease-deficient viral mutant. We demonstrate that the exonuclease activity of UL12 is essential for the production of viral progeny and thus provides an attractive, druggable enzymatic target.

Comparative effect of sesamin and episesamin on the activity and gene expression of enzymes in fatty acid oxidation and synthesis in rat liver.

Sesamin is one of the most abundant lignans in sesame seed. Episesamin, a geometrical isomer of sesamin, is not a naturally occurring compound and is formed during the refining process of non-roasted sesame seed oil. We compared the physiological activities of these compounds in affecting hepatic fatty acid metabolism in rat liver. Rats were fed either a control diet free of lignan or diets containing 0.2% of sesamin or episesamin for 15 days. These lignans increased the mitochondrial and peroxisomal palmitoyl-CoA oxidation rates. However, the magnitude of the increases was greater with episesamin than with sesamin. Sesamin caused 1.7- and 1.6-fold increases in mitochondrial and peroxisomal activity, respectively, while episesamin increased these values 2.3- and 5.1-fold. These lignans also increased the activity and gene expression of various fatty acid oxidation enzymes. Again, the increase was much more exaggerated with episesamin (1.5- to 14-fold) than with sesamin (1.3- to 2.8-fold). Diets containing sesamin and episesamin lowered the activity and gene expression of hepatic lipogenic enzymes to one-half of those obtained in the animals fed a lignan-free diet. However, no significant differences in these parameters were seen between rats fed sesamin and episesamin. Responses to sesamin and episesamin of hepatic lipogenesis are, therefore, considerably different from those observed in fatty acid oxidation. These results show that the physiological activity of the commercial sesamin preparation containing equivalent amounts of both sesamin and episesamin in increasing hepatic fatty acid oxidation observed previously was mainly ascribable to that of episesamin but not to sesamin.