The specificity determinants for susceptibility to resistance by the Fv1 n and b alleles map to amino acid 110 of the murine leukemia virus CA protein. To study the interaction between Fv1 and CA, we examined changes in CA resulting in the loss of susceptibility to Fv1 resistance in naturally occurring NB-and NR-tropic viruses. A variety of amino acid changes affecting Fv1 tropism were identified, at CA positions 82, 92 to 95, 105, 114, and 117, and they all were mapped to the apparent exterior of virion-associated CA. These amino acids may form a binding surface for Fv1.The Fv1 gene is one of a series of mouse genes, originally described in the early 1970s, that control the susceptibility of mice to murine leukemia virus (MLV) infection (32,34 nr , found in a few inbred strains of mice and apparently also in some wild mice, restricts B-tropic MLV and some, but not all, N-tropic viruses (28,48). In this paper, we will refer to N-tropic viruses that are not restricted by Fv1 nr as being NR tropic.Fv1 acts in a cell-autonomous manner to restrict virus replication (44), but the precise mechanism for restriction is unclear. It has been shown that viral replication is blocked at a stage after virus entry into the cell and before the integration of newly synthesized viral DNA into the host genome (22, 41). The block to infection is not absolute in vitro, but the number of infected cells is reduced by a factor of 50 to 1,000 (17). When expressed at natural levels, e.g., in mouse fibroblast lines, neither Fv1 n nor Fv1 b shows significant in vitro restriction of NB-tropic MLV.Genetic studies initially suggested that the target for Fv1 restriction is the MLV capsid (CA) protein (20, 43). Subsequent studies indicated that viral tropism is determined by a pair of adjacent amino acids, at positions 109 and 110, in CA (10, 40). A more recent study has shown that position 110 is the most important residue for N and B tropism (29). N-tropic MLV has an Arg residue at this position, and B-tropic MLV has a Glu residue. The determinants for NB and NR tropism have not been fully characterized.The Fv1 gene was cloned a few years ago (3) and was found to have sequence similarity to a family of endogenous retroviruses called HERV-L (60% identity over 1.3 kb) or MuERV-L (1, 3). Based on its position within the element and the presence of a major homology region (3), Fv1 apparently encodes a Gag-related protein. Gag proteins bind tightly to each other via interaction domains during virus assembly (35), which suggests a possible mechanism for Fv1's action on MLV CA (16). To date, however, there is no direct evidence for the binding of Fv1 to CA. Biochemical analyses are greatly complicated by the extremely low natural expression levels of Fv1 in vivo. We have therefore taken a genetic approach to analyzing the viral determinants of NB and NR tropism, using a rapid fluorescence-activated cell sorting (FACS)-based approach for Fv1 testing (5), in an attempt to delineate the region(s) of CA that interacts with Fv1. MATERIALS AND METHODS Cel...
The herpes simplex virus type 1 (HSV-1) ICP34.5 gene is a neurovirulence gene in mice. In addition, some ICP34.5 mutants have been reported to have a reduced efficiency of induced reactivation as measured by in vitro explantation of latently infected mouse ganglia. However, since spontaneous reactivation is almost nonexistent in mice, nothing has been reported on the effect of ICP34.5 mutants on spontaneous reactivation in vivo. To examine this, we have deleted both copies of the ICP34.5 neurovirulence gene from a strain of HSV-1 (McKrae) that has a high spontaneous reactivation rate in rabbits and used this mutant to infect rabbit eyes. All rabbits infected with the ICP34.5 mutant virus (d34.5) survived, even at challenge doses greater than 4 ؋ 10 7 PFU per eye. In contrast, a 200-fold-lower challenge dose of 2 ؋ 10 5 PFU per eye was lethal for approximately 50% of rabbits infected with either the wild-type McKrae parental virus or a rescued ICP34.5 mutant in which both copies of the ICP34.5 gene were restored. In mice, the 50% lethal dose of the ICP34.5 mutant was over 10 6 PFU, compared with a value of less than 10 PFU for the rescued virus. The ICP34.5 mutant was restricted for replication in rabbit and mouse eyes and mouse trigeminal ganglia in vivo. The spontaneous reactivation rate in rabbits for the mutant was 1.4% as determined by culturing tear films for the presence of reactivated virus. This was more than 10-fold lower than the spontaneous reactivation rate determined for the rescued virus (19.6%) and was highly significant (P < 0.0001, Fisher exact test). Southern analysis confirmed that the reactivated virus retained both copies of the ICP34.5 deletion. Thus, this report demonstrates that (i) the ICP34.5 gene, known to be a neurovirulence gene in mice, is also important for virulence in rabbits and (ii) in vivo spontaneous reactivation of HSV-1 in the rabbit ocular model, although reduced, can occur in the absence of the ICP34.5 gene.
This study examined the microbicidal activity of 222-nm UV radiation (UV222), which is potentially a safer alternative to the 254-nm UV radiation (UV254) that is often used for surface decontamination. Spores and/or growing and stationary-phase cells of Bacillus cereus, Bacillus subtilis, Bacillus thuringiensis, Staphylococcus aureus, and Clostridioides difficile and a herpesvirus were all killed or inactivated by UV222 and at lower fluences than with UV254. B. subtilis spores and cells lacking the major DNA repair protein RecA were more sensitive to UV222, as were spores lacking their DNA-protective proteins, the α/β-type small, acid-soluble spore proteins. The spore cores’ large amount of Ca2+-dipicolinic acid (∼25% of the core dry weight) also protected B. subtilis and C. difficile spores against UV222, while spores’ proteinaceous coat may have given some slight protection against UV222. Survivors among B. subtilis spores treated with UV222 acquired a large number of mutations, and this radiation generated known mutagenic photoproducts in spore and cell DNA, primarily cyclobutane-type pyrimidine dimers in growing cells and an α-thyminyl-thymine adduct termed the spore photoproduct (SP) in spores. Notably, the loss of a key SP repair protein markedly decreased spore UV222 resistance. UV222-treated B. subtilis spores germinated relatively normally, and the generation of colonies from these germinated spores was not salt sensitive. The latter two findings suggest that UV222 does not kill spores by general protein damage, and thus, the new results are consistent with the notion that DNA damage is responsible for the killing of spores and cells by UV222. IMPORTANCE Spores of a variety of bacteria are resistant to common decontamination agents, and many of them are major causes of food spoilage and some serious human diseases, including anthrax caused by spores of Bacillus anthracis. Consequently, there is an ongoing need for efficient methods for spore eradication, in particular methods that have minimal deleterious effects on people or the environment. UV radiation at 254 nm (UV254) is sporicidal and commonly used for surface decontamination but can cause deleterious effects in humans. Recent work, however, suggests that 222-nm UV (UV222) may be less harmful to people than UV254 yet may still kill bacteria and at lower fluences than UV254. The present work has identified the damage by UV222 that leads to the killing of growing cells and spores of some bacteria, many of which are human pathogens, and UV222 also inactivates a herpesvirus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.