Genetically variable triplet repeats in a RING-finger ORF of Helicoverpa species baculoviruses

Nucleotide sequence analysis of the Helicoverpa zea S-type nucleopolyhedrovirus (HzSNPV) genomic interval between the polh and iel genes has revealed an open reading frame (HOAR ORF) that contains a complex A 1-T rich triplet repeat region (RAT-repeats). HOAR ORF is predicted to encode an acidic, arginine residue rich. 712 aa protein, with a C3HC4 (RING-finger) zinc binding motif. RAT-repeats, distributed over 450 bp. consist of GAT. AAT, and GTT codons, correspond to Asp, Asn and Val residues which display an extreme codon bias not seen with nine other genes of this virus. A survey of four other (field) isolates of Helicoverpa sp. NPVs confirms a high incidence of mutation in the RAT-repeat region. A 158-bp conserved block, homologous to the pe38-ien promoter of AcMNPV, was identified upstream of HOAR ORF. The sub-region of the genome in which HOAR ORF is located is susceptible to rearrangement.