IDENTIFICATION OF THE PRIMARY STRUCTURE AND THE CODING CAPACITY OF THE GENOME OF INSECT IRIDESCENT VIRUS TYPE-6 BETWEEN THE GENOME COORDINATE-0.310 AND COORDINATE-0.347 (7990-BP)

The primary structure and the coding capacity of the insect iridescent virus type 6 - Chilo iridescent virus (CIV) - were determined between the genome coordinates 0.310 (EcoRI site) and 0.347 (ClaI site). The EcoRI CIV DNA fragment M (7.1 kb; 0.310-0.345 map units) harbors one o ut of at least six loci of DNA replication origins which is located at nucleotide position 485-513. The identification of the structural pro perties and the coding capacity of the EcoRI CIV DNA fragment M was ca rried out by DNA nucleotide sequencing, computer-aided sequence analys is and DNA/RNA hybridization. The EcoRI CIV DNA fragment M (7,099 bp; 71.14% A + T and 28.86% G + C) possesses two clusters of five tandemly organized repetitive DNA elements with complex structural arrangement s (R1-R5) which are located between nucleotide positions 3272-3350 and 3403-3414. The analysis of the DNA sequences of the EcoRI CIV DNA fra gment M revealed the presence of six open reading frames (ORFs 1-6). T wo out of six detected putative proteins are of particular interest. O RF-2 was found to be terminated at nucleotide position 366 (TAA) withi n the DNA sequence of the EcoRI CIV DNA fragment L (0.345-0.381 map un its; 7.4 kb). The analysis of ORF-2 (1,051 amino acids; 120 kD) reveal ed homologies to several DNA-directed RNA polymerases. ORF-6 encodes a protein (606 amino acids; 69 kD) which is related to a group of yeast , Drosophila and mammalian proteins of a distinct family of putative D NA and/or RNA helicases belonging to the 'DEAD/H' superfamily. The tra nscriptional activity of the EcoRI CIV DNA fragment M was determined b y DNA/RNA hybridization experiments. These analyses revealed the exist ence of three RNA transcripts of about 3.4 kb (t1), 1.8 kb (t2) and 1. 2 kb (t3) which agree with the predicted size of the expected RNA tran scripts from ORF-2 (1,051 amino acids; 3.1 kb) and ORF-6 (606 amino ac ids; 1.8 kb).