The structure of P4 procapsids produced by coexpression of capsid and external scaffolding proteins.
The double-stranded DNA bacteriophage P4 has a T = 4 icosahedral arrangement of the gpN capsid protein derived from the P2 helper phage. The precursor procapsids in addition contain an external scaffold made up of the P4-encoded Sid protein. High yields of pure P4 procapsids have been obtained by coexpressing the gpN and Sid proteins from a chimeric plasmid. Biochemical measurements show that the ratio of gpN to Sid in the procapsids is 2:1, corresponding to 120 copies of Sid per procapsid particle. A reconstruction of the P4 procapsid, made from 213 particle images to an effective resolution of about 21 A, greatly improves on the previously determined P4 procapsid structures. The structure shows a T = 4 capsid shell and a unique tandem arrangement of 120 copies of chilli-shaped Sid monomers, which form trimers and dimers on the procapsid surface.
Institute of Molecular Agrobiology, Singapore. dokland@ima.org.sg
Terje
T
Dokland
Sifang
S
Wang
Björn H
BH
Lindqvist
D001435:Bacteriophages / Q000737:chemistry* / Q000648:ultrastructure; D002213:Capsid / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D020285:Cryoelectron Microscopy; D008958:Models, Molecular; D010957:Plasmids; D015678:Viral Structural Proteins / Q000737:chemistry* / Q000378:metabolism; D019065:Virus Assembly
D015678:Viral Structural Proteins