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The sophisticated tail structures of DNA bacteriophages play essential roles in life cycles. Podoviruses P22 and Sf6 have short tails consisting of multiple proteins, among which is a tail adaptor protein that connects the portal protein to the other tail proteins. Assembly of the tail has been shown to occur in a sequential manner to ensure proper molecular interactions, but the underlying mechanism remains to be understood. Here, we report the high-resolution structure of the tail adaptor protein gp7 from phage Sf6. The structure exhibits distinct distribution of opposite charges on two sides of the molecule. A gp7 dodecameric ring model shows an entirely negatively charged surface, suggesting that the assembly of the dodecamer occurs through head-to-tail interactions of the bipolar monomers. The N-terminal helix-loop structure undergoes rearrangement compared with that of the P22 homolog complexed with the portal, which is achieved by repositioning of two consecutive repeats of a conserved octad sequence motif. We propose that the conformation of the N-terminal helix-loop observed in the Sf6-gp7 and P22 portal:gp4 complex represents the pre- and postassembly state, respectively. Such motif repositioning may serve as a conformational switch that creates the docking site for the tail nozzle only after the assembly of adaptor protein to the portal. In addition, the C-terminal portion of gp7 shows conformational flexibility, indicating an induced fit on binding to the portal. These results provide insight into the mechanistic role of the adaptor protein in mediating the sequential assembly of the phage tail. [ABSTRACT FROM AUTHOR]

2D and 3D cryo-electron microscopy, together with adsorption kinetics assays of ΦCb13 and ΦCbK phage-infected Caulobacter crescentus, provides insight into the mechanisms of infection. ΦCb13 and ΦCbK actively interact with the flagellum and subsequently attach to receptors on the cell pole. We present evidence that the first interaction of the phage with the bacterial flagellum takes place through a filament on the phage head. This contact with the flagellum facilitates concentration of phage particles around the receptor (i.e., the pilus portals) on the bacterial cell surface, thereby increasing the likelihood of infection. Phage head filaments have not been well characterized and their function is described here. Phage head filaments may systematically underlie the initial interactions of phages with their hosts in other systems and possibly represent a widespread mechanism of efficient phage propagation. [ABSTRACT FROM AUTHOR]

Perhaps the simplest of biological timing systems, bacteriophage holins accumulate during the phage morphogenesis period and then trigger to permeabilize the cytoplasmic membrane with lethal holes; thus, terminating the infection cycle. Canonical holins form very large holes that allow nonspecific release of fully-folded proteins, but a recently discovered class of holins, the pinholins, make much smaller holes, or pinholes, that serve only to depolarize the membrane. Here, we interrogate the structure of the prototype pinholin by negative-stain transmission electron-microscopy, cysteine-accessibility, and chemical cross-linking, as well as by computational approaches. Together, the results suggest that the pinholin forms symmetric heptameric structures with the hydrophilic surface of one transmembrane domain lining the surface of a central channel ≈15 A in diameter. The structural model also suggests a rationale for the prehole state of the pinholin, the persistence of which defines the duration of the viral latent period. and for the sensitivity of the holin timing system to the energized state of the membrane. [ABSTRACT FROM AUTHOR]

The multisubunit RNA polymerase (RNAP) in bacteria consists of a catalytically active core enzyme (α2ββ'ω) complexed with a σ factor that is required for promoter-specific transcription initiation. During early elongation the stability of interactions between σ and core decreases, in part because of the nascent RNA-mediated destabilization of an interaction between region 4 of σ and the flap domain of the β-subunit (β-flap). The nascent RNA-mediated destabilization of the σ region 4/β-flap interaction is required for the bacteriophage λ Q antiterminator protein (λQ) to engage the RNAP holoenzyme. Here, we provide an explanation for this requirement by showing that λQ establishes direct contact with the β-flap during the engagement process, thus competing with σ70 region 4 for access to the β-flap. We also show that λQ's affinity for the β-flap is calibrated to ensure that λQ activity is restricted to the λ late promoter PR'. Specifically, we find that strengthening the λQ/β-flap interaction allows λQ to bypass the requirement for specific cis-acting sequence elements, a λQ-DNA binding site and a RNAP pause-inducing element, that normally ensure λQ is recruited exclusively to transcription complexes associated with PR'. Our findings demonstrate that the β-flap can serve as a direct target for regulators of elongation. [ABSTRACT FROM AUTHOR]

Coliphage N4 virion RNA polymerase (vRNAP), which is injected into the host upon infection, transcribes the phage early genes from promoters that have a 5-bp stem-3 nt loop hairpin structure. Here, we describe the 2.0-Å resolution x-ray crystal structure of N4 mini-vRNAP, a member of the T7-like, single-unit RNAP family and the minimal component having all RNAP functions of the full-length vRNAP. The structure resembles a "fisted right hand" with Fingers, Palm and Thumb subdomains connected to an N-terminal domain. We established that the specificity loop extending from the Fingers along with W129 of the N-terminal domain play critical roles in hairpin-promoter recognition. A comparison with the structure of the T7 RNAP initiation complex reveals that the pathway of the DNA to the active site is blocked in the apo-form vRNAP, indicating that vRNAP must undergo a large-scale conformational change upon promoter DNA binding and explaining the highly restricted promoter specificity of vRNAP that is essential for phage early transcription. [ABSTRACT FROM AUTHOR]

Presents information a study that described cloning and characterization of three self-splicing introns that are inserted in a late transcribed open reading frame in the genome of bacteriophage Twort. Materials and methods; Results; Discussion.

Presents information on a study which examined the role of Cys... zinc-binding motif to bacteriophage T7 primase in single-stranded DNA. Materials and methods; Results and discussion.

Reports on DNA and predicted protein sequence similarities among genes of double-stranded DNA bacteriophages and prophages spanning a broad phylogenetic range of host bacteria. Establishment of genetic connections among the lambdoid phages; Presentation of a model for the genetic structure and dynamics of the global phage population.

Offers information on a study regarding rap proteins structure involved in bacteriophages lambda recombination. Materials and methodology; Results; Discussion on the results.

Compares the deoxythymidine triphosphatase (dTTPase) mechanism of the catalytic sites of bacteriophage T7 helicase with the binding change mechanism of the ATP synthase. Hydrolysis of dTTP; Noncatalytic nucleotide binding sites of the hexamer; Rotational catalysis and comparison to the F1-ATPase.

Proposes a model that explains the stoichiometric packaging of the chromosome of a bacteriophage with a genome of three unique double-stranded RNA segments. Ordered switches in packaging specificity and RNA synthesis; Bacterial strains and plasmids; Determination of the amount of RNA within the procapsid.

Describes the initiation of the replication of complementary-strand DNA in filamentous bacteriophages by a primer RNA synthesized at the minus-strand origin. Escherichia coli RNA polymerase holoenzyme containing the omega70 subunit; Affinity of RNA polymerase in vitro to the origin; LacUV5 promoter.

Demonstrates the use of a self-sustained terminal protein-primed DNA amplification system to describe in vitro evolutionary changes affecting maintenance of the genome size of bacteriophage phi29. Generation and amplification of short palindromic molecules containing an inverted duplication of an original DNA end; Template-switching mechanism.

The article reports that the researchers have useds Listeria monocytogenes L-form bacteria to reactivate the synthetic bacteriophage DNA using process genome rebooting. The authorsused Listeria L-form cells to reboot Listeria phage genomes and phages from other Gram-positive bacteria including Bacillus and Staphylococcus.