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PubMed1994

Identification of genes encoding zinc finger proteins, non-histone chromosomal HMG protein homologue, and a putative GTP phosphohydrolase in the genome of Chilo iridescent virus.

Five RNA transcripts of about 1.2 to 1.7 kilobases were mapped to a part of the genome of insect iridescent virus type 6 (Chilo iridescent virus; CIV) between genome coordinates 0.832 and 0.856 within the EcoRI DNA fragment F. The nucleotide sequence of this particular region (5702 base pairs) of the CIV genome was determined. The DNA sequence contains a number of perfect direct, inverted, and palindromic repeats including three clusters of tandemly organized repetitive DNA elements located between the nucleotide positions 1534 to 1566, 3720 to 3780, and 4350 to 4450. Eight long open reading frames (ORFs; EF1 to 8) were detected in the sequenced region of the CIV genome. ORF EF1 encodes a putative protein of 221 amino acid residues (aa) that is closely related to eukaryotic nonhistone chromosomal proteins of the high mobility group (HMG) superfamily. Virus encoded homologues of HMG proteins have not been reported so far. The EF2 gene product (145 aa) contains a specific zinc finger motif and belongs to a distinct group of identified and putative zinc finger proteins including a second putative protein (239 aa) of CIV encoded in the EcoRI DNA fragment Y (1984 bp; 0.381 to 0.391 viral map units). The product of EF6 (127 aa) is related to D250 ORF product of African swine fever virus (ASFV) and belongs to the recently described protein family sharing a highly conserved sequence motif with bacterial antimutator GTP phosphohydrolase MutT. Thus the sequenced region of the CIV genome encodes three putative proteins which may be directly involved in the replication and/or transcription of the viral DNA.

Amino Acid Sequence↗
PubMed1994

Expression of Semliki Forest virus nsP1-specific methyltransferase in insect cells and in Escherichia coli.

We have expressed the Semliki Forest virus (SFV)-specific nonstructural protein nsP1 both in insect cells and in Escherichia coli in the absence of other viral proteins. A substantial amount of nsP1 was synthesized in Sf9 cells infected with the recombinant Autographa californica nuclear polyhedrosis virus (AcNPV) AcNPV-nsP1. These cells had a high level of guanine-7-methyltransferase activity compared with that of wild-type AcNPV-infected cells. The methyltransferase activity and nsP1 were mostly in the mitochondrial pellet fraction (P15). The enzymatic activity was increased by treatment with deoxycholate (DOC), as in the case of SFV-infected BHK cells. The material released by DOC treatment from P15 of the AcNPV-nsP1-infected cells was analyzed by gel filtration and sucrose gradient centrifugation. Both the methyltransferase activity and nsP1 were in aggregates. nsP1 expressed in E. coli at 37 degrees C sedimented at 15,000 x g, whereas after expression at 15 degrees C, both nsP1 and methyltransferase activity were in the supernatant fraction. Paradoxically, the activity from E. coli was completely inhibited by Triton X-100 and DOC. Sucrose gradient analysis showed that even the "soluble" nsP1-methyltransferase was in aggregates. The methyltransferase activities in the P15 fractions of SFV-infected BHK cells and AcNPV-nsP1-infected Sf9 cells and in E. coli catalyzed linear incorporation of the [3H]methyl group from S-adenosylmethionine to GTP for a 60-min period. The enzymes from the three sources had similar substrate specificities and Km values for S-adenosylmethionine. In addition to GTP, they all methylated dGTP and GpppG, but not m7GTP or GpppA, or in vitro-transcribed RNAs with GpppA and GpppG caps. The unique properties of SFV-specific nsP1 methyltransferase are discussed.

Animals↗