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Abstract: Bacteriophage øX174 morphogenesis requires two scaffolding proteins: an internal species, similar to those employed in other viral systems, and an external species, which is more typically associated with satellite viruses. The current model of øX174 assembly is based on structural and in vivo data. During morphogenesis, 240 copies of the external scaffolding protein mediate the association of 12 pentameric particles into procapsids. The hypothesized pentameric intermediate, the 12S⁎ particle, contains 16 proteins: 5 copies each of the coat, spike and internal scaffolding proteins and 1 copy of the DNA pilot protein. Assembly naïve 12S⁎ particles and external scaffolding oligomers, most likely tetramers, formed procapsid-like particles in vitro, suggesting that the 12S⁎ particle is a bona fide assembly intermediate and validating the current model of procapsid morphogenesis. The in vitro system required a crowding agent, was influenced by the ratio of the reactants and was most likely driven by hydrophobic forces. While the system reported here shared some characteristics with other in vitro internal scaffolding protein-mediated systems, it displayed unique features. These features most likely reflect external scaffolding protein-mediated morphogenesis and the øX174 procapsid structure, in which external scaffolding–scaffolding protein interactions, as opposed to coat–coat protein interactions between pentamers, constitute the primary lattice-forming contacts. [Copyright &y& Elsevier]

The article focuses on the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 genome-editing technique that help in finding how bacteria take snapshots of DNA as well as of RNA. Topics discussed include usage of a bacterial defense system in the technology; fusion of Casl protein, a scaffolding protein, in type III CRISPR systems; and views of Andrew Fire, biologist at the Stanford University, on the same.