Arch Virol (2004) 149: 1971–1983
An mRNA region of the canine distemper virus fusion protein
gene lacking AUG codons can promote protein expression
, L. Zipperle
, R. Wittek
, and A. Zurbriggen
Department of Clinical Veterinary Medicine, University of Bern, Bern, Switzerland
Institut de Biotechnologie, University of Lausanne, Lausanne, Switzerland
Received December 29, 2003; accepted March 17, 2004
Published online May 25, 2004
Summary. Canine distemper virus (CDV) produces a glycosylated type I fusion
protein (F) with an internal hydrophobic signal sequence beginning around 115
residues downstream of the ﬁrst AUG used for translation initiation. Cleavage of
the signal sequence yields the F0 molecule, which is cleaved into the F1 and F2
subunits. Surprisingly, when all in-frame AUGs located in the ﬁrst third of the
F gene were mutated a protein of the same molecular size as the F0 molecule
was still expressed from both the Onderstepoort (OP) and A75/17-CDV F genes.
We designated this protein, which is initiated from a non-AUG codon protein Fx.
Site-directed mutagenesis allowed to identify codon 85, a GCC codon coding for
alanine, as the most likely position from which translation initiation of Fx occurs in
OP-CDV. Deletion analysis demonstrated that at least 60 nucleotides upstream of
the GCC codon are required for efﬁcient Fx translation. This sequence is GC-rich,
suggesting extensive folding. Secondary structure may therefore be important for
translation initiation at codon 85.
Canine distemper virus (CDV) is a member of the genus Morbillivirus within
the family Paramyxovirus and is closely related to Measles virus. CDV is highly
infectious for dogs and other carnivores, as well as for some marine mammals.
Distemper is characterized by virus persistence in the central nervous system,
frequently leading to a demyelinating disease [23, 24]. The genome of CDV
consists in a negative single-stranded RNA about 15,500 nucleotides. Six mRNAs
coding for 8 different proteins are transcribed from the genome.
The envelope of morbilliviruses contains two glycoproteins: the attachment
(H) and fusion protein (F). The F protein is a type I glycoprotein, which is important
for promoting membrane fusion and cell-to-cell spread [16, 21]. The fusion protein