Showing papers by "Bryan R. Cullen published in 1990"

Structure-function analyses of the HTLV-I Rex and HIV-1 Rev RNA response elements: insights into the mechanism of Rex and Rev action.

Abstract: The ability of the Rex protein of the type I human T-cell leukemia virus (HTLV-I) to regulate expression of the retroviral gag and env structural genes post-transcriptionally is critically dependent on the presence of a Rex response element (RexRE). This cis-regulatory sequence is located within the retroviral 3' long terminal repeat and coincides with a predicted, highly stable RNA stem-loop structure. Rex action requires both the overall secondary structure intrinsic to the RexRE and specific sequences from one small subregion of this large structure. This small subregion likely forms a protein-binding site for Rex or a cellular RNA-binding factor. Whereas Rex can functionally replace the Rev protein of the type 1 human immunodeficiency virus (HIV-1) through its interaction with the analogous Rev response element (RevRE), distinct subregions of this HIV-1 RNA element mediate the responses to Rex and Rev. Strikingly, Rex acts as a dominant repressor of Rev action, following the deletion of the Rex responsive subregion of the RevRE. Similarly, Rev inhibits Rex function in a dominant manner when the Rev responsive subregion of the RevRE is deleted. Together, these findings suggest that Rex and Rev not only interact with their respective RNA response elements but also may either form mixed inactive multimers or interact with a common cellular factor(s). If binding of a common host protein is involved, this factor likely plays a central role either in spliceosome assembly or nuclear RNA transport.

A highly conserved RNA folding region coincident with the Rev response element of primate immunodeficiency viruses

Abstract: A series of unusual folding regions (UFR) immediately 3' to the cleavage site of the outer membrane protein (OMP) and transmembrane protein (TMP) were detected in the envelope gene RNA of the human immunodeficiency virus (HIV-1, HIV-2) and simian immunodeficiency virus (SIV) by an extensive Monte Carlo simulation. These RNA secondary structures were predicted to be both highly stable and statistically significant. In the calculation, twenty-five different sequence isolates of HIV-1, three isolates of HIV-2 and eight sequences of SIV were included. Although significant sequence divergence occurs in the env coding regions of these viruses, a distinct UFR of 234-nt is consistently located ten nucleotides 3' to the cleavage site of the OMP/TMP in HIV-1, and a 216-nt UFR occurs forty-six and forty-nine nucleotides downstream from the OMP/TMP cleavage site of HIV-2 and SIV, respectively. Compensatory base changes in the helical stem regions of these conserved RNA secondary structures are identified. These results support the hypothesis that these special RNA folding regions are functionally important and suggest that the role of this sequence as the Rev response element (RRE) is mediated by secondary structure as well as primary RNA sequence.

Visna virus encodes a post-transcriptional regulator of viral structural gene expression

Abstract: Visna virus is an ungulate lentivirus that is distantly related to the primate lentiviruses, including human immunodeficiency virus type 1 (HIV-1). Replication of HIV-1 and of other complex primate retroviruses, including human T-cell leukemia virus type I (HTLV-I), requires the expression in trans of a virally encoded post-transcriptional activator of viral structural gene expression termed Rev (HIV-1) or Rex (HTLV-I). We demonstrate that the previously defined L open reading frame of visna virus encodes a protein, here termed Rev-V, that is required for the cytoplasmic expression of the incompletely spliced RNA that encodes the viral envelope protein. Transactivation by Rev-V was shown to require a cis-acting target sequence that coincides with a predicted RNA secondary structure located within the visna virus env gene. However, Rev-V was unable to function by using the structurally similar RNA target sequences previously defined for Rev or Rex and, therefore, displays a distinct sequence specificity. Remarkably, substitution of this visna virus target sequence in place of the HIV-1 Rev response element permitted the Rev-V protein to efficiently rescue the expression of HIV-1 structural proteins, including Gag, from a Rev- proviral clone. These results suggest that the post-transcriptional regulation of viral structural gene expression may be a characteristic feature of complex retroviruses.

Multivalent repressor of gene function

Abstract: Transdominant repressors of viral gene phenotypic expression derived from the rev gene product of HIV-1 or the rex gene product of HTLV-I and corresponding mutated genes are described, having the capability of repressing the Rev function in HIV-1 and/or the Rex function in HTLV-I and HTLV-II. Transient gene expression analysis of a series of missense and deletion mutants has been used. Some of the mutants found repress both the Rev and the Rex function and are thus active in more than one viral species. Transdominant viral mutants represent a promising new class of anti-viral agents. Cellular expression of these transdominant inhibitors may be used in such therapeutic approaches as intracellular immunization in order to protect cells against the deleterious effects of viral, e.g. HIV-1 infection.

The HIV-1 REV Trans-Activator is a Sequence Specific RNA Binding Protein

Abstract: The pathogenic human retrovirus, human immunodeficiency virus type 1 (HIV-1), is the major etiologic agent of the acquired immunodeficiency syndrome (AIDS) (Fauci, 1988). HIV-1, along with the related primate immunodeficiency viruses, HIV-2 and simian immunodeficiency virus (SIV), is a member of a subfamily of retroviruses known as lentiviruses. Other members of this subfamily include visna virus, caprine arthritis encephalitis virus (CAEV), equine infectious anemia virus (EIAV) and feline immunodeficiency virus (FIV). Lentivirus infection of the susceptible host typically results in a prolonged and chronic disease state affecting the immune and nervous systems as well as cells in a variety of other tissues (reviewed by Haase, 1986). Interestingly, these viruses display complex patterns of gene expression that are very different from those of the extensively studied Type C family of retroviruses. Specifically, proviral activation from a frequently extended period of latency is followed by a pattern of viral gene expression that is markedly temporal. During this time a number of differentially spliced viral transcripts may be observed.