Human Immunodeficiency Virus Retroviruses Research Articles

PREVALENCE OF DEATHS IN ELDERLY PEOPLE WITH ACQUIRED HUMAN IMMUNODEFICIENCY SYNDROME IN THE NORTHEAST REGION

Acquired Immunodeficiency Syndrome (AIDS) is a disease of the immune system caused by the retrovirus HIV ― from English, Human Immunodeficiency Virus and the present study aims to analyze the prevalence and cases of AIDS deaths in the elderly population in the Northeastern state, from 2015 to 2019. This is a descriptive study obtained from the Health Information System provided by TABNET, referring to elderly people with HIV/AIDS, who were notified in the northeast region in the period from 2015 to 2017. Thus, in the years 2015 and 2017, there were 76 deaths from the Human Immunodeficiency Virus (HIV) reported in the Northeast region of Brazil. Of these, 22 cases of deaths were related to the elderly population of Bahia, and the State of Alagoas had the lowest number, just 2 deaths. Regarding AIDS cases identified in the Northeast state, from 2015 to 2019, 1,204 cases of AIDS were reported. Absolutely, the states that reported the most were Bahia (233 cases), Pernambuco (224 cases), Maranhão (190 cases) and Ceará (185 cases). Based on above considerations, prevention campaigns aimed only at the elderly population, health professionals and caregivers unprepared are necessary to provide information regarding sexuality and sexual practices for elderly people in the Federative Units and regions.

In Silico Prediction of Biomarkers from Amaranthus tricolor (L) Targeted against HIV-1 Protease

Acquired immunodeficiency syndrome is caused by a retrovirus human immunodeficiency virus (HIV). Resistance to antiviral drugs is alarming in antiretroviral therapy and medical management of HIV-infected patients. Thus, identifying novel antiviral drugs is critical and medicinal plants are an excellent source for such discoveries. The current study aimed to isolate and characterize the chemical constituents from leaves of Amaranthus tricolor (L) and to discover novel HIV-1 protease inhibitors. Amaranthus tricolor methanolic extract (ATME) was fractionated into chloroform and aqueous phases. The chloroform fraction was separated by column chromatography using mobile phase n-hexane: ethyl acetate (6:4 v/v). Among various fractions, SOWIS-III was purified and studied for structural interpretation. The compounds were docked with HIV-1 protease as a drug target. The structural interpretation of the SOWIS-III fraction was identified as flavanol glycoside 24-methylene cycloartanol and SOWIS-P as a gallic acid derivative methyl 3,4,5-trihydroxybenzoate. The docking studies of 24-Methylenecycloartanol and HIV-1 protease showed 10 amino acid interactions with the estimated free energy of binding of -10.14 kcal/mol and the antiviral activity depicted as 36.88 nM. Methyl 3,4,5-trihydroxybenzoate and HIV-1 protease show five amino acid interactions with the estimated free energy of binding of -5.03 kcal/mol with 205.24 μM estimated antiviral activity. Hence, 24-methylene cycloartanol and methyl 3,4,5-trihydroxybenzoate can serve as drug candidates for HIV.

The emerging role of perivascular cells (pericytes) in viral pathogenesis.

Viruses may exploit the cardiovascular system to facilitate transmission or within-host dissemination, and the symptoms of many viral diseases stem at least in part from a loss of vascular integrity. The microvascular architecture is comprised of an endothelial cell barrier ensheathed by perivascular cells (pericytes). Pericytes are antigen-presenting cells (APCs) and play crucial roles in angiogenesis and the maintenance of microvascular integrity through complex reciprocal contact-mediated and paracrine crosstalk with endothelial cells. We here review the emerging ways that viruses interact with pericytes and pay consideration to how these interactions influence microvascular function and viral pathogenesis. Major outcomes of virus-pericyte interactions include vascular leakage or haemorrhage, organ tropism facilitated by barrier disruption, including viral penetration of the blood-brain barrier and placenta, as well as inflammatory, neurological, cognitive and developmental sequelae. The underlying pathogenic mechanisms may include direct infection of pericytes, pericyte modulation by secreted viral gene products and/or the dysregulation of paracrine signalling from or to pericytes. Viruses we cover include the herpesvirus human cytomegalovirus (HCMV, Human betaherpesvirus 5), the retrovirus human immunodeficiency virus (HIV; causative agent of acquired immunodeficiency syndrome, AIDS, and HIV-associated neurocognitive disorder, HAND), the flaviviruses dengue virus (DENV), Japanese encephalitis virus (JEV) and Zika virus (ZIKV), and the coronavirus severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2; causative agent of coronavirus disease 2019, COVID-19). We touch on promising pericyte-focussed therapies for treating the diseases caused by these important human pathogens, many of which are emerging viruses or are causing new or long-standing global pandemics.

An analytical pipeline for identifying and mapping the integration sites of HIV and other retroviruses

BackgroundAll retroviruses, including human immunodeficiency virus (HIV), must integrate a DNA copy of their genomes into the genome of the infected host cell to replicate. Although integrated retroviral DNA, known as a provirus, can be found at many sites in the host genome, integration is not random. The adaption of linker-mediated PCR (LM-PCR) protocols for high-throughput integration site mapping, using randomly-sheared genomic DNA and Illumina paired-end sequencing, has dramatically increased the number of mapped integration sites. Analysis of samples from human donors has shown that there is clonal expansion of HIV infected cells and that clonal expansion makes an important contribution to HIV persistence. However, analysis of HIV integration sites in samples taken from patients requires extensive PCR amplification and high-throughput sequencing, which makes the methodology prone to certain specific artifacts.ResultsTo address the problems with artifacts, we use a comprehensive approach involving experimental procedures linked to a bioinformatics analysis pipeline. Using this combined approach, we are able to reduce the number of PCR/sequencing artifacts that arise and identify the ones that remain. Our streamlined workflow combines random cleavage of the DNA in the samples, end repair, and linker ligation in a single step. We provide guidance on primer and linker design that reduces some of the common artifacts. We also discuss how to identify and remove some of the common artifacts, including the products of PCR mispriming and PCR recombination, that have appeared in some published studies. Our improved bioinformatics pipeline rapidly parses the sequencing data and identifies bona fide integration sites in clonally expanded cells, producing an Excel-formatted report that can be used for additional data processing.ConclusionsWe provide a detailed protocol that reduces the prevalence of artifacts that arise in the analysis of retroviral integration site data generated from in vivo samples and a bioinformatics pipeline that is able to remove the artifacts that remain.

Yagya Therapy for Managing Inferiority & Insecurity feeling of HIV+ /AIDS Patients

The present study was designed to manage the feeling of inferiority & insecurity of HIV+ /AIDS patients through Yagya therapy. HIV+/AIDS is a type of immunodeficiency which is caused by the retrovirus HIV (Human Immunodeficiency Virus). Eighty diagnosed HIV+/AIDS subjects in the range of 12 to 40 years were selected form Haridwar, Dehradun, and Roorkee districts on the basis of score obtained on the Inferiority and Insecurity Questionnaire (Pati, 1976). These subjects were assigned randomly to two conditions namely, control (N=40, 20 males and 20 females) and experimental (N=40, 20 males and 20 females). The subjects in the experimental group were only exposed to Yayga therapy practices about one hour daily for six months. A between group design was used in the present study and obtained data were statistically analyzed through t-test. The finding reveals that Yagya therapy significantly reduces the levels of inferiority and insecurity feeling of patients. Conclusion: Yagya therapy is an effective therapy for managing inferiority & insecurity feeling of HIV+ patients.

Polymorphisms in the APOBEC3G gene of Chinese rhesus macaques affect resistance to ubiquitination and degradation mediated by HIV-2 Vif.

Animal cells have multiple innate effector mechanisms that inhibit viral replication. For the pathogenic retrovirus human immunodeficiency virus 1 (HIV-1), there are widely expressed restriction factors, such as APOBEC3 proteins, tetherin/BST2, SAMHD1 and MX2, as well as TRIM5α. We previously found that the TRIM5α gene clearly affects SIVmac or HIV-2 replication, but the major determinant of the combinatorial effect caused by multiple host restriction factors is still not fully clear. APOBEC3G (apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like 3G), a host restriction factor that restricts HIV replication by causing cytosine deamination, can be targeted and degraded by the SIV/HIV-1/HIV-2 accessory protein Vif. Although rhesus macaques are widely used in HIV/AIDS research, little is known regarding the impact of APOBEC3G gene polymorphisms on viral Vif-mediated ubiquitin degradation in Chinese-origin rhesus macaques. In this study, we therefore genotyped APOBEC3G in 35 Chinese rhesus macaques. We identified a novel transcript and 27 APOBEC3G polymorphisms, including 20 non-synonymous variants and 7 synonymous mutation sites, of which 10 were novel. According to the predicted structure of the A3G protein, we predicted that the E88K and G212D mutations, both on the surface of the A3G protein, would have a significant effect on Vif-induced A3G degradation. However, an in vitro overexpression assay showed that these mutations did not influence HIV-2-Vif-mediated degradation of APOBEC3G. Unexpectedly, another polymorphism L71R, conferred resistance to Vif-mediated ubiquitin degradation, strongly suggesting that L71R might play an important role in antiviral defense mechanisms.

Implications of oxidative stress on viral pathogenesis.

Reactive species are frequently formed after viral infections. Antioxidant defences, including enzymatic and non-enzymatic components, protect against reactive species, but sometimes these defences are not completely adequate. An imbalance in the production of reactive species and the body's inability to detoxify these reactive species is referred to as oxidative stress. The aim of this review is to analyse the role of oxidative stress in the pathogenesis of viral infections and highlight some major therapeutic approaches that have gained importance, with regards to controlling virus-induced oxidative injury. Attention will be focused on DNA viruses (papillomaviruses, hepadnaviruses), RNA viruses (flaviviruses, orthomyxoviruses, paramyxoviruses, togaviruses) and retroviruses (human immunodeficiency virus). In general, viruses cause an imbalance in the cellular redox environment, which depending on the virus and the cell can result in different responses, e.g. cell signaling, antioxidant defences, reactive species, and other processes. Therefore, the modulation of reactive species production and oxidative stress potentially represents a novel pharmacological approach for reducing the consequences of viral pathogenesis.

Severe Acute Respiratory Syndrome Coronavirus ORF7a Inhibits Bone Marrow Stromal Antigen 2 Virion Tethering through a Novel Mechanism of Glycosylation Interference.

Severe acute respiratory syndrome (SARS) emerged in November 2002 as a case of atypical pneumonia in China, and the causative agent of SARS was identified to be a novel coronavirus, severe acute respiratory syndrome coronavirus (SARS-CoV). Bone marrow stromal antigen 2 (BST-2; also known as CD317 or tetherin) was initially identified to be a pre-B-cell growth promoter, but it also inhibits the release of virions of the retrovirus human immunodeficiency virus type 1 (HIV-1) by tethering budding virions to the host cell membrane. Further work has shown that BST-2 restricts the release of many other viruses, including the human coronavirus 229E (hCoV-229E), and the genomes of many of these viruses encode BST-2 antagonists to overcome BST-2 restriction. Given the previous studies on BST-2, we aimed to determine if BST-2 has the ability to restrict SARS-CoV and if the SARS-CoV genome encodes any proteins that modulate BST-2's antiviral function. Through an in vitro screen, we identified four potential BST-2 modulators encoded by the SARS-CoV genome: the papain-like protease (PLPro), nonstructural protein 1 (nsp1), ORF6, and ORF7a. As the function of ORF7a in SARS-CoV replication was previously unknown, we focused our study on ORF7a. We found that BST-2 does restrict SARS-CoV, but the loss of ORF7a leads to a much greater restriction, confirming the role of ORF7a as an inhibitor of BST-2. We further characterized the mechanism of BST-2 inhibition by ORF7a and found that ORF7a localization changes when BST-2 is overexpressed and ORF7a binds directly to BST-2. Finally, we also show that SARS-CoV ORF7a blocks the restriction activity of BST-2 by blocking the glycosylation of BST-2. The severe acute respiratory syndrome coronavirus (SARS-CoV) emerged from zoonotic sources in 2002 and caused over 8,000 infections and 800 deaths in 37 countries around the world. Identifying host factors that regulate SARS-CoV pathogenesis is critical to understanding how this lethal virus causes disease. We have found that BST-2 is capable of restricting SARS-CoV release from cells; however, we also identified a SARS-CoV protein that inhibits BST-2 function. We show that the SARS-CoV protein ORF7a inhibits BST-2 glycosylation, leading to a loss of BST-2's antiviral function.

Role of Cyclic GMP-AMP Synthase in Sensing Human Immunodeficiency Virus

*Cyclic guanosine monophosphate adenosine monophosphate (cGAMP) synthase (cGAS) detects human immunodeficiency virus (HIV) and produces cGAMP to induce cytokines. Reverse transcribed DNA of HIV is critical for triggering innate immune responses as inhibitor of HIV reverse transcriptase blocked the induction of interferon-β by the virus. Furthermore, knockout of cGAS in human or mouse cell lines abrogated the production of cytokines by HIV infection highlighting the essential role of cGAS in detection of HIV and other retroviruses.

Human MX2 is an interferon-induced post-entry inhibitor of HIV-1 infection

Animal cells harbour multiple innate effector mechanisms that inhibit virus replication. For the pathogenic retrovirus human immunodeficiency virus type-1 (HIV-1), these include widely expressed restriction factors1 such as APOBEC3 proteins2, TRIM5α3, tetherin/BST24,5 and SAMHD16,7, as well as additional factors that are stimulated by type-1 interferon (IFN)8,9,10,11,12,13,14. Here, we employ both ectopic expression and gene silencing experiments to define the human dynamin-like, IFN-induced guanosine triphosphatase (GTPase), myxovirus resistance 2 (MX2 or MxB) protein, as a potent inhibitor of HIV-1 infection and as a major effector of IFNα-mediated resistance to HIV-1 infection. MX2 suppresses infection by all HIV-1 strains tested, has similar to modest effects on divergent simian immunodeficiency viruses (SIVs), and does not inhibit other retroviruses such as murine leukaemia virus (MLV). The capsid (CA) region of the viral Gag protein dictates susceptibility to MX2, and the block to infection occurs at a late post-entry step with the nuclear accumulation and chromosomal integration of nascent viral cDNA both being suppressed. Finally, human MX1 (or MxA), a closely related protein that has long been recognised as a broadly acting inhibitor of RNA/DNA viruses, including the orthomyxovirus influenza A virus15,16, does not affect HIV-1,whereas MX2 is ineffective against influenza virus. MX2 is therefore a cell-autonomous, anti-HIV-1 resistance factor whose purposeful mobilisation may represent a new therapeutic approach for the treatment of HIV/AIDS.

-defensin Genomic Copy Number Is Associated With HIV Load and Immune Reconstitution in Sub-Saharan Africans

AIDS, caused by the retrovirus human immunodeficiency virus (HIV), is the leading cause of death of economically active people (age, 15-59 years) in sub-Saharan Africa. The host genetic variability of immune response to HIV and immune reconstitution following initiation of highly active antiretroviral therapy (HAART) is poorly understood. Here we focused on copy number variation of the β-defensin genes, which have been shown to have anti-HIV activity, and are important chemoattractants for Th17 lymphocytes via the chemokine receptor CCR6. We determined β-defensin gene copy number for 1002 Ethiopian and Tanzanian patients. We show that higher β-defensin copy number variation is associated with increased HIV load prior to HAART (P=.005) and poor immune reconstitution following initiation of HAART (P=.003). We suggest a model where variable amounts of β-defensin expression by mucosal cells, due to gene copy number variation, alters the efficacy of recruitment of Th17 lymphocytes to the site of infection, altering the dynamics of infection.

Retroviruses Human Immunodeficiency Virus and Murine Leukemia Virus Are Enriched in Phosphoinositides

Retroviruses acquire a lipid envelope during budding from the membrane of their hosts. Therefore, the composition of this envelope can provide important information about the budding process and its location. Here, we present mass spectrometry analysis of the lipid content of human immunodeficiency virus type 1 (HIV-1) and murine leukemia virus (MLV). The results of this comprehensive survey found that the overall lipid content of these viruses mostly matched that of the plasma membrane, which was considerably different from the total lipid content of the cells. However, several lipids are enriched in comparison to the composition of the plasma membrane: (i) cholesterol, ceramide, and GM3; and (ii) phosphoinositides, phosphorylated derivatives of phosphatidylinositol. Interestingly, microvesicles, which are similar in size to viruses and are also released from the cell periphery, lack phosphoinositides, suggesting a different budding mechanism/location for these particles than for retroviruses. One phosphoinositide, phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)], has been implicated in membrane binding by HIV Gag. Consistent with this observation, we found that PI(4,5)P(2) was enriched in HIV-1 and that depleting this molecule in cells reduced HIV-1 budding. Analysis of mutant virions mapped the enrichment of PI(4,5)P(2) to the matrix domain of HIV Gag. Overall, these results suggest that HIV-1 and other retroviruses bud from cholesterol-rich regions of the plasma membrane and exploit matrix/PI(4,5)P(2) interactions for particle release from cells.

Triaryl Pyrazoline Compound Inhibits Flavivirus RNA Replication

Triaryl pyrazoline {[5-(4-chloro-phenyl)-3-thiophen-2-yl-4,5-dihydro-pyrazol-1-yl]-phenyl-methanone} inhibits flavivirus infection in cell culture. The inhibitor was identified through high-throughput screening of a compound library using a luciferase-expressing West Nile (WN) virus infection assay. The compound inhibited an epidemic strain of WN virus without detectable cytotoxicity (a 50% effective concentration of 28 microM and a compound concentration of >or=300 microM required to reduce 50% cell viability). Besides WN virus, the compound also inhibited other flaviviruses (dengue, yellow fever, and St. Louis encephalitis viruses), an alphavirus (Western equine encephalitis virus), a coronavirus (mouse hepatitis virus), and a rhabdovirus (vesicular stomatitis virus). However, the compound did not suppress an orthomyxovirus (influenza virus) or a retrovirus (human immunodeficiency virus type 1). Mode-of-action analyses in WN virus showed that the compound did not inhibit viral entry or virion assembly but specifically suppressed viral RNA synthesis. To examine the mechanism of inhibition of dengue virus, we developed two replicon systems for dengue type 1 virus: (i) a stable cell line that harbored replicons containing a luciferase reporter and a neomycin phosphotransferase selection marker and (ii) a luciferase-expressing replicon that could differentiate between viral translation and RNA replication. Analyses of the compound in the dengue type 1 virus replicon systems showed that it weakly suppressed viral translation but significantly inhibited viral RNA synthesis. Overall, the results demonstrate that triaryl pyrazoline exerts a broad spectrum of antiflavivirus activity through potent inhibition of viral RNA replication. This novel inhibitor could be developed for potential treatment of flavivirus infection.

Programmed ribosomal frameshifting in HIV-1 and the SARS–CoV

Ribosomal frameshifting is a mechanism of gene expression used by several RNA viruses to express replicase enzymes. This article focuses on frameshifting in two human pathogens, the retrovirus human immunodeficiency virus type 1 (HIV-1) and the coronavirus responsible for severe acute respiratory syndrome (SARS). The nature of the frameshift signals of HIV-1 and the SARS–CoV will be described and the impact of this knowledge on models of frameshifting will be considered. The role of frameshifting in the replication cycle of the two pathogens and potential antiviral therapies targeting frameshifting will also be discussed.

A critique of the Montagnier evidence for the HIV/AIDS hypothesis

In 1983 Luc Montagnier and his colleagues claimed to have discovered a novel retrovirus presently known as human immunodeficiency virus (HIV). By 1984 HIV was almost universally accepted to be the cause of AIDS. However, 20 years later, HIV cannot account for the phenomena for which the retroviral hypothesis was proposed, namely, Kaposi's sarcoma, decrease in T4 lymphocytes and thus the opportunistic infections in AIDS patients which were assumed to be the direct results of this decrease. Agents other than HIV to which patients belonging to the AIDS risk groups are exposed cause decrease in T4 cells. Neither have the main predictions of the HIV hypothesis been fulfilled. HIV seropositivity in the developed countries still remains restricted to the original high risk groups, no HIV vaccine exists, and no successful animal model has been developed. In this communication, we critically analyse the evidence which in 1983 was claimed to prove the existence of HIV. The phenomena which Montagnier and his colleagues considered proof for the existence of HIV are detection of reverse transcriptase activity; the presence of retrovirus-like particles in the culture; immunological reactivity between proteins from the culture supernatant which, in sucrose density gradients, banded at the density of 1.16 g/ml (“purified virus”) and antibodies in a patient's (BRU) serum. Reverse transcriptase activity can be found in viruses other than retroviruses and in all normal cells. Reverse transcription can be brought about not only by the enzyme reverse transcriptase but also by normal, cellular DNA polymerases. Retrovirus-like particles are ubiquitous in cultures not infected with retroviruses, especially in conditions employed by Montagnier et al. From the reaction between proteins in the “purified virus” and antibodies in the patient serum Montagnier concluded that the proteins were HIV proteins and the antibodies were HIV antibodies. Since all antibodies are polyspecific, from such a reaction it is not possible to define the origin of even one reactant let alone both. Even if this were possible, since Montagnier's “purified virus” did not contain particles with the “morphology typical of retroviruses”, the proteins cannot be retroviral. We conclude that, these phenomena are non-specific to retroviruses and thus cannot be considered proof for the existence of a unique retrovirus HIV.

Prevalence of human T-cell leukemia virus types I and II in Switzerland.

The retroviruses human immunodeficiency virus (HIV)-1/2 and human T-cell leukemia virus (HTLV)-I/II share modes of transmission, suggesting that efforts to monitor the current HIV-1 epidemic in Switzerland should be complemented by assessment of HTLV-I/II prevalence. This study presents an updated evaluation of HTLV-I/II infection among groups within the Swiss population polarized towards either low or increased risk of infection. Archived serum and peripheral blood mononuclear cell (PBMC) samples were examined for evidence of HTLV-I/II infection by enzyme-linked immunosorbant assay (ELISA), type-specific Western blot, type-specific polymerase chain reaction (PCR), DNA sequence analysis, and virus culture. Among blood donations obtained from low-risk Swiss donors, we report a complete lack of HTLV-II infection and the occurrence of HTLV-I infection limited to a prevalence of 0.079 per 100,000 (1/1,266,466). Among high-risk HIV-positive persons and HIV-negative persons at increased risk of HIV-infection, we report a focus of HTLV-I and HTLV-II infection at prevalence rates of 62 per 100,000 (1/1,620) and 309 per 100,000 (5/1,620), respectively. The finding of low HTLV-I/II prevalence among Swiss blood donors and containment of HTLV-I/II infection within known risk-groups does not support initiation of HTLV-I/II screening for Swiss blood, tissue, and organ donations.

Mechanisms of CD4+ T lymphocyte cell death in human immunodeficiency virus infection and AIDS

AIDS, caused by the retroviruses human immunodeficiency virus type 1 and type 2 (HIV-1 and HIV-2), has reached pandemic proportions. Therefore, it is critical to understand how HIV causes AIDS so that appropriate therapies can be formulated. Primarily, HIV infects and kills CD4(+) T lymphocytes, which function as regulators and amplifiers of the immune response. In the absence of effective anti-retroviral therapy, the hallmark decrease in CD4(+) T lymphocytes during AIDS results in a weakened immune system, impairing the body's ability to fight infections or certain cancers such that death eventually ensues. The major mechanism for CD4(+) T cell depletion is programmed cell death (apoptosis), which can be induced by HIV through multiple pathways. Death of HIV-infected cells can result from the propensity of infected lymphocytes to form short-lived syncytia or from an increased susceptibility of the cells to death. However, the apoptotic cells appear to be primarily uninfected bystander cells and are eradicated by two different mechanisms: either a Fas-mediated mechanism during activation-induced cell death (AICD), or as a result of HIV proteins (Tat, gp120, Nef, Vpu) released from infected cells stimulating apoptosis in uninfected bystander cells. There is also evidence that as AIDS progresses cytokine dysregulation occurs, and the overproduction of type-2 cytokines (IL-4, IL-10) increases susceptibility to AICD whereas type-1 cytokines (IL-12, IFN-gamma) may be protective. Clearly there are multiple causes of CD4(+) T lymphocyte apoptosis in AIDS and therapies that block or decrease that death could have significant clinical benefit.

HIV‐1 Protease: Mechanism and Drug Discovery

AbstractFor Abstract see ChemInform Abstract in Full Text.

Roles of uracil-DNA glycosylase and dUTPase in virus replication.

Herpesviruses and poxviruses are known to encode the DNA repair enzyme uracil-DNA glycosylase (UNG), an enzyme involved in the base excision repair pathway that specifically removes the RNA base uracil from DNA, while at least one retrovirus (human immunodeficiency virus type 1) packages cellular UNG into virus particles. In these instances, UNG is implicated as being important in virus replication. However, a clear understanding of the role(s) of UNG in virus replication remains elusive. Herpesviruses, poxviruses and some retroviruses encode dUTPase, an enzyme that can minimize the misincorporation of uracil into DNA. The encoding of dUTPase by these viruses also implies their importance in virus replication. An understanding at the molecular level of how these viruses replicate in non-dividing cells should provide clues to the biological relevance of UNG and dUTPase function in virus replication.

The retroviruses human immunodeficiency virus type 1 and Moloney murine leukemia virus adopt radically different strategies to regulate promoter-proximal polyadenylation.

Maximal gene expression in retroviruses requires that polyadenylation in the 5' long terminal repeat (LTR) is suppressed. In human immunodeficiency virus type 1 (HIV-1) the promoter-proximal poly(A) site is blocked by interaction of U1 snRNP with the closely positioned major splice donor site (MSD) 200 nucleotides downstream. Here we investigated whether the same mechanism applies to down-regulate 5' LTR polyadenylation in Moloney murine leukemia virus (MoMLV). Although the same molecular architecture is present in both viruses, the MoMLV poly(A) signal in the 5' LTR is active whether or not the MSD is mutated. This surprising difference between the two retroviruses is not due to their actual poly(A) signals or MSD sequences, since exchange of either element between the two viral sequences does not alter their ability to regulate 5' LTR poly(A) site use. Instead we demonstrate that sequence between the cap and AAUAAA is required for MSD-dependent poly(A) regulation in HIV-1, indicating a key role for this part of the LTR in poly(A) site suppression. We also show that the MoMLV poly(A) signal is an intrinsically weak RNA-processing signal. This suggests that in the absence of a poly(A) site suppression mechanism, MoMLV is forced to use a weak poly(A) signal.