Related Experiment Video
Updated: Jun 3, 2026

Iterative Optimization of DNA Duplexes for Crystallization of SeqA-DNA Complexes
Published on: November 1, 2012
Structure of bacteriophage phi29 head fibers has a supercoiled triple repeating helix-turn-helix motif
1Department of Biological Sciences, Purdue University, 240 S. Martin Jischke Drive, West Lafayette, IN 47907-2032, USA.
Abstract:
The tailed bacteriophage 29 capsid is decorated with 55 fibers attached to quasi-3-fold symmetry positions. Each fiber is a homotrimer of gene product 8.5 (gp8.5) and consists of two major structural parts, a pseudohexagonal base and a protruding fibrous portion that is about 110 Å in length. The crystal structure of the C-terminal fibrous portion (residues 112-280) has been determined to a resolution of 1.6 Å. The structure is about 150 Å long and shows three distinct structural domains designated as head, neck, and stem. The stem region is a unique three-stranded helix-turn-helix supercoil that has not previously been described. When fitted into a cryoelectron microscope reconstruction of the virus, the head structure corresponded to a disconnected density at the distal end of the fiber and the neck structure was located in weak density connecting it to the fiber. Thin section studies of Bacillus subtilis cells infected with fibered or fiberless 29 suggest that the fibers might enhance the attachment of the virions onto the host cell wall.
Related Concept Videos
DNA Bacteriophages
Lytic Cycle of Bacteriophages
Viral Replication: Lytic Cycle
Lysogenic Cycle of Bacteriophages
DNA Helicases
The Replisome
The synthesis of the leading and lagging strands is a highly coordinated process. To explain this, the “Trombone model” was proposed by Bruce Alberts in 1980. The DNA loop formation starts when a primer is synthesized on the parent lagging strand. The loop grows with the...

