The Effects of Packaged, but Misguided, Single-Stranded DNA Genomes Are Transmitted to the Outer Surface of the ϕX174 Capsid.

Most icosahedral viruses condense their genomes into volumetrically constrained capsids. However, concurrent genome biosynthesis and packaging are specific to single-stranded DNA (ssDNA) viruses. ssDNA genome packaging combines elements found in both double-stranded DNA (dsDNA) and ssRNA systems.

Mutagenic Analysis of a DNA Translocating Tube's Interior Surface.

Bacteriophage ϕX174 uses a decamer of DNA piloting proteins to penetrate its host. These proteins oligomerize into a cell wall-spanning tube, wide enough for genome passage. While the inner surface of the tube is primarily lined with inward-facing amino acid side chains containing amide and guanidinium groups, there is a 28 Å-long section near the tube's C-terminus that does not exhibit this motif.

Finally, a Role Befitting A: Strongly Conserved, Unessential Microvirus A* Proteins Ensure the Product Fidelity of Packaging Reactions.

In microviruses, 60 copies of the positively charged DNA binding protein J guide the single-stranded DNA genome into the icosahedral capsid. Consequently, ∼12% of the genome is icosahedrally ordered within virions. Although the internal volume of the ϕX174, G4, and α3 capsids are nearly identical, their genome lengths vary widely from 5,386 (ϕX174) to 6,067 (α3) nucleotides.

Recessive Host Range Mutants and Unsusceptible Cells That Inactivate Virions without Genome Penetration: Ecological and Technical Implications.

Although microviruses do not possess a visible tail structure, one vertex rearranges after interacting with host lipopolysaccharides. Most examinations of host range, eclipse, and penetration were conducted before this "host-induced" unique vertex was discovered and before DNA sequencing became routine. Consequently, structure-function relationships dictating host range remain undefined.

Structural changes of tailless bacteriophage ΦX174 during penetration of bacterial cell walls.

Unlike tailed bacteriophages, which use a preformed tail for transporting their genomes into a host bacterium, the ssDNA bacteriophage ΦX174 is tailless. Using cryo-electron microscopy and time-resolved small-angle X-ray scattering, we show that lipopolysaccharides (LPS) form bilayers that interact with ΦX174 at an icosahedral fivefold vertex and induce single-stranded (ss) DNA genome ejection. The structures of ΦX174 complexed with LPS have been determined for the pre- and post-ssDNA ejection states.

Coat Protein Mutations That Alter the Flux of Morphogenetic Intermediates through the ϕX174 Early Assembly Pathway.

Two scaffolding proteins orchestrate ϕX174 morphogenesis. The internal scaffolding protein B mediates the formation of pentameric assembly intermediates, whereas the external scaffolding protein D organizes 12 of these intermediates into procapsids. Aromatic amino acid side chains mediate most coat-internal scaffolding protein interactions.

Structure-Function Analysis of the ϕX174 DNA-Piloting Protein Using Length-Altering Mutations.

Unlabelled: Although the ϕX174 H protein is monomeric during procapsid morphogenesis, 10 proteins oligomerize to form a DNA translocating conduit (H-tube) for penetration. However, the timing and location of H-tube formation are unknown. The H-tube's highly repetitive primary and quaternary structures made it amenable to a genetic analysis using in-frame insertions and deletions.

The evolution of genes within genes and the control of DNA replication in microviruses.

Single-stranded DNA(ssDNA) viral life cycles must balance double-stranded DNA (dsDNA) and ssDNA biosynthesis. Previously published in vitro results suggest that microvirus C and host cell SSB proteins play antagonistic roles to achieve this balance. To investigate this in vivo, microvirus DNA replication was characterized in cells expressing cloned C or ssb genes, which would presumably alter the C:SSB protein ratios.

Icosahedral bacteriophage ΦX174 forms a tail for DNA transport during infection.

Prokaryotic viruses have evolved various mechanisms to transport their genomes across bacterial cell walls. Many bacteriophages use a tail to perform this function, whereas tail-less phages rely on host organelles. However, the tail-less, icosahedral, single-stranded DNA ΦX174-like coliphages do not fall into these well-defined infection processes.