The principal structural component of a retrovirus particle is the Gag protein. Retroviral genomic RNAs contain a ‘packaging signal’ (‘Ψ') and are packaged in virus particles with very high selectivity. However, if no genomic RNA is present, Gag assembles into particles containing cellular mRNA molecules. The mechanism by which genomic RNA is normally selected during virus assembly is not understood. We previously reported (Comas-Garcia et al., 2017) that at physiological ionic strength, recombinant HIV-1 Gag binds with similar affinities to RNAs with or without Ψ, and proposed that genomic RNA is selectively packaged because binding to Ψ initiates particle assembly more efficiently than other RNAs. We now present data directly supporting this hypothesis. We also show that one or more short stretches of unpaired G residues are important elements of Ψ; Ψ may not be localized to a single structural element, but is probably distributed over >100 bases.
Nano/micromotors
based on biodegradable and biocompatible polymers
represent a progressively developing group of self-propelled artificial
devices capable of delivering biologically active compounds to target
sites. The majority of these machines are micron sized, and biologically
active compounds are simply attached to their surface. Micron-sized
devices cannot enter cells, but they provide rapid velocity, which
scales down with the size of the device; nanosized devices can enter
cells, but their velocity is negligible. An advanced hierarchical
design of the micro/nanodevices is an important tool in the development
of functional biocompatible transport systems and their implementation
in real in vivo applications. In this work, we demonstrate a “mothership”
concept, whereby self-propelled microrobots transport smaller cargo-carrying
nanorobots that are released by enzymatic degradation.
Budding is the final step of the late phase of retroviral life cycle. It begins with the interaction of Gag precursor with plasma membrane (PM) through its N-terminal domain, the matrix protein (MA). However, single genera of Retroviridae family differ in the way how they interact with PM. While in case of Lentiviruses (e.g., human immunodeficiency virus) the structural polyprotein precursor Gag interacts with cellular membrane prior to the assembly, Betaretroviruses [Mason-Pfizer monkey virus (M-PMV)] first assemble their virus-like particles (VLPs) in the pericentriolar region of the infected cell and therefore, already assembled particles interact with the membrane. Although both these types of retroviruses use similar mechanism of the interaction of Gag with the membrane, the difference in the site of assembly leads to some differences in the mechanism of the interaction. Here we describe the interaction of M-PMV MA with PM with emphasis on the structural aspects of the interaction with single phospholipids.
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