Comparison of the eIF-2alpha homologous proteins of seven ranaviruses (Iridoviridae).
The alpha-subunit of the eukaryotic initiation factor 2 (eIF-2alpha) is a key component of the translation machinery of the cell. In response to cellular stress such as viral infections, eIF-2alpha is phosphorylated by double-stranded RNA-dependent protein kinase (PKR) leading to the inhibition of cellular protein synthesis. The importance of eIF-2alpha as a regulatory mechanism for protein synthesis is illustrated by the wide variety of strategies employed by viruses to down-regulate PKR. Thus, Vaccinia virus encodes K3L protein, which resembles eIF-2alpha and acts as a pseudo-substrate inhibitor of PKR. Nucleotide sequencing of the genome of epizootic haematopoietic necrosis virus (EHNV), a member of the genus ranavirus of Iridoviridae, has revealed an eIF-2alpha equivalent gene. We have cloned and sequenced eIF-2alpha genes of several iridoviruses of fishes and frogs. The eIF-2alpha open reading frames and deduced proteins of the iridoviruses investigated exhibit a high degree of homology of both nucleotide and amino acid sequences. At the N-terminus, the iridoviral eIF-2alpha shows significant homology to the N-termini of cellular initiation factor 2-alpha of various species, to full-length poxviral eIF-2alpha proteins, and to the S1 domain of ribosomal proteins. Comparison of amino acid sequences of corresponding iridoviral proteins with eIF-2alpha homologous proteins of poxviruses and eukaryotes has revealed a high conservation of motifs. A phylogenetic analysis of eukaryotic eIF-2alpha and poxvirus and iridovirus eIF-2alpha sequences has demonstrated the relationship of these iridoviruses. In order to investigate the role of the eIF-2alpha equivalent, respective genes have been expressed in prokaryotic and eukaryotic (insect, fish and chicken cell) systems. The iridoviral eIF-2alpha protein has a molecular weight of 31 kDa and is cytoplasmic. The cellular and viral protein synthesis of iridoviruses is probably regulated by a mechanism similar to that of Vaccinia virus. Frog-virus 3, the type species of the genus ranavirus of Iridoviridae, has a unique translational efficiency and, moreover, down-regulates the cellular protein synthesis of infected cells.
Essbauer
S
S
Institute of Zoology, Fishery Biology and Fish Diseases, LMU University of Munich, Muenchen, Germany. sandra.essbauer@micro.vetmed.uni-muenchen.de
Bremont
M
M
Ahne
W
W
D000595:Amino Acid Sequence; D000818:Animals; D001001:Anura; D015139:Blotting, Southern; D015852:Eukaryotic Initiation Factor-2 / Q000737:chemistry / Q000235:genetics*; D005399:Fishes; D006801:Humans; D007372:Interferons / Q000502:physiology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010802:Phylogeny; D017995:Ranavirus / Q000235:genetics* / Q000302:isolation & purification; D017385:Sequence Homology
D015852:Eukaryotic Initiation Factor-2; D007372:Interferons