| Autor: |
Marvik, Ole J., Dokland, Terje, Nokling, Rebekka H., Jacobsen, Erik, Larsen, Turid, Lindqvist, Bjorn H. |
| Zdroj: |
JMB Online (Journal of Molecular Biology); August 4,1995, Vol. 251 Issue: 1 p59-75, 17p |
| Abstrakt: |
Although the phages P2 and P4 build their capsids from the same precursor, the product of the P2Ngene, the two capsids differ in size: P2 build a 60 nm,T= 7 capsid from 420 subunits, whereas P4 makes a 45 nm,T= 4 capsid from 240 subunits. This difference leads to substantial changes in shell geometry and subunit interactions. Previous results have demonstrated that the P4sidgene is responsible for the assembly of P4-sized shells. We have used cryo-electron microscopy and image reconstruction to determine the structure of a putative assembly intermediate of P4 capsids, producedin vivofrom cloned genes. We demonstrate that Sid forms a P4-specific scaffold with icosahedral symmetry on the outside of the procapsid-like particles. The Sid molecules (60 or 120 copies) from lofty arches that interact with the gpN hexamers on the icosahedral 2-fold axes, and connect as trimers over the 3-fold axes, forming a continuous dodecahedrally shaped outer cage. The gpN shell inside the Sid cage is approximately 40 nm wide, consistent with the previously suggested maturational expansion. The main difference with respect to the mature P4 capsids is found in the hexamers, which appear strongly elongated and more protruding than in the mature shell. These and previous results are discussed in the light of a model for regulation of capsid size. |
| Databáze: |
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