Exceptional flexibility in the sequence requirements for coronavirus small envelope protein function.
The small envelope protein (E) plays a role of central importance in the assembly of coronaviruses. This was initially established by studies demonstrating that cellular expression of only E protein and the membrane protein (M) was necessary and sufficient for the generation and release of virus-like particles. To investigate the role of E protein in the whole virus, we previously generated E gene mutants of mouse hepatitis virus (MHV) that were defective in viral growth and produced aberrantly assembled virions. Surprisingly, however, we were also able to isolate a viable MHV mutant (DeltaE) in which the entire E gene, as well as the nonessential upstream genes 4 and 5a, were deleted. We have now constructed an E knockout mutant that confirms that the highly defective phenotype of the DeltaE mutant is due to loss of the E gene. Additionally, we have created substitution mutants in which the MHV E gene was replaced by heterologous E genes from viruses spanning all three groups of the coronavirus family. Group 2 and 3 E proteins were readily exchangeable for that of MHV. However, the E protein of a group 1 coronavirus, transmissible gastroenteritis virus, became functional in MHV only after acquisition of particular mutations. Our results show that proteins encompassing a remarkably diverse range of primary amino acid sequences can provide E protein function in MHV. These findings suggest that E protein facilitates viral assembly in a manner that does not require E protein to make sequence-specific contacts with M protein.
Kuo
Lili
L
David Axelrod Institute, Wadsworth Center, NY State Department of Health, New Scotland Avenue, Albany, NY 12201-2002, USA. masters@wadsworth.org
Hurst
Kelley R
KR
Masters
Paul S
PS
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002415:Cats; D002460:Cell Line; D004279:DNA, Viral / Q000235:genetics; D015870:Gene Expression; D005814:Genes, Viral; D051379:Mice; D008969:Molecular Sequence Data; D006517:Murine hepatitis virus / Q000235:genetics* / Q000502:physiology*; D009154:Mutation; D010641:Phenotype; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D005760:Transmissible gastroenteritis virus / Q000235:genetics / Q000502:physiology; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D014779:Virus Replication
D004279:DNA, Viral; D011993:Recombinant Fusion Proteins; D014759:Viral Envelope Proteins