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Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
Morphogenesis of Bacteriophage ϕ29, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818388/9781555810535_Chap59-1.gif /docserver/preview/fulltext/10.1128/9781555818388/9781555810535_Chap59-2.gifAbstract:
Bacteriophages are very useful models for studying the protein-derived principles of form determination in virus assembly. Bacteriophage models cannot be ignored because of the assembly of the virus tail at the prohead portal vertex or connector, the entry point of double-stranded DNA. Bacteriophage ø29 of Bacillus subtilis, illustrated in the family portrait with bacteriophage T2 of Escherichia coli, features simplicity, efficient in vitro assembly, and advanced genetic and biochemical characterizations. This chapter emphasizes ø29 structure and the mechanisms of prohead assembly and DNA packaging, the major thrusts of current ø29 research in Minneapolis. The basic problem of ø29 morphogenesis is the mechanism by which a prolate shell of particular dimensions is assembled from subunits that are also capable of being assembled into incorrect structures. Mutants of asporogenous B. subtilis that cannot assemble ø29 (vam) were selected by the use of antibodies that reacted more strongly with the free connectors than with the portal vertex of proheads or phage. Bacteriophage DNA-packaging machines seem to have in common two packaging proteins and a connector with sixfold symmetry. Restriction enzyme digestion of DNA molecules extracted from DNase I-treated proheads shows that DNA-gp3 packaging is oriented with respect to the physical map. A gyrase action would be needed to generate supercoiled DNA for packaging.
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Family portrait of phages ϕ29 and T2. Magnification, x 428,000.
Family portrait of phages ϕ29 and T2. Magnification, x 428,000.
Pathway of ϕ29 morphogenesis. Proteins composing a structure are listed below it. Prohead II and the 11¯, 12¯, and 13¯ particles are true intermediates in the pathway. The 10¯, 7¯, and 9¯ structures shown below the main pathway are abortive structures. Particle a has been observed only in restrictive sus12(716) infection together with the 12¯ particle; its composition is inferred from morphology.
Pathway of ϕ29 morphogenesis. Proteins composing a structure are listed below it. Prohead II and the 11¯, 12¯, and 13¯ particles are true intermediates in the pathway. The 10¯, 7¯, and 9¯ structures shown below the main pathway are abortive structures. Particle a has been observed only in restrictive sus12(716) infection together with the 12¯ particle; its composition is inferred from morphology.
Three views of the modified ? = 3 model of the ϕ29 prohead according to S. Casjens and R. Hendrix. The model contains 30 hexamers (light) and 11 pentamers (dark) of the major capsid protein. The panel on the right shows a view of the base, where the connector (not shown) is attached. The computer-generated schematics are by E. Egelman.
Three views of the modified ? = 3 model of the ϕ29 prohead according to S. Casjens and R. Hendrix. The model contains 30 hexamers (light) and 11 pentamers (dark) of the major capsid protein. The panel on the right shows a view of the base, where the connector (not shown) is attached. The computer-generated schematics are by E. Egelman.
Secondary structure of ϕ29 pRNA derived by phylogenetic analysis ( 6 ). A through F, helical stems. Residues conserved in the ϕ29-???, M2-Nf, SF5, and GA1 pRNA sequences are designated in boldface letters.
Secondary structure of ϕ29 pRNA derived by phylogenetic analysis ( 6 ). A through F, helical stems. Residues conserved in the ϕ29-???, M2-Nf, SF5, and GA1 pRNA sequences are designated in boldface letters.