N-terminal deletions of the phiX174 external scaffolding protein affect the timing and fidelity of assembly

Virology. 2009 Apr 10;386(2):303-9. doi: 10.1016/j.virol.2009.01.030. Epub 2009 Feb 23.


The first alpha-helices of Microviridae external scaffolding proteins function as coat protein substrate specificity domains. Mutations in this helix can lengthen the lag phase before progeny production. 5' deletion genes, encoding N-terminal deletion proteins, were constructed on plasmids and in the øX174 genome. Proteins lacking the first seven amino acids were able to rescue a nullD mutant when expressed from a plasmid. However, the lag phase before progeny production was lengthened. The øX174 mutant with the corresponding genomic gene grew very poorly. The molecular basis of the defective phenotype was complex. External scaffolding protein levels were reduced compared to wild-type and most of the viral coat protein in mutant infected cells appears to be siphoned off the assembly pathway. Second-site suppressors of the growth defects were isolated and appear to act via two different mechanisms. One class of suppressors most likely acts by altering mutant external scaffolding protein expression while the second class of suppressors appears to act on the level of protein-protein interactions.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacteriophage phi X 174 / genetics*
  • Bacteriophage phi X 174 / metabolism
  • Bacteriophage phi X 174 / physiology*
  • Mutagenesis
  • Sequence Deletion
  • Viral Structural Proteins / genetics
  • Viral Structural Proteins / metabolism*
  • Virus Assembly*


  • Viral Structural Proteins