Pattern of transcription of the genome of equine infectious anemia virus

The pattern of expression of the equine infectious anemia virus (EIAV) genome in a persistently infected canine cell line was determined. Five EIAV-specific transcripts (8.2, 5.0, 4.0, 2, and 1.8 kilobases [kb]) were detected by using subgenomic restriction enzyme fragments of EIAV DNA and EIAV-specific oligonucleotides as probes. The 8.2-kb mRNA could be shown to represent viral genomic RNA, whereas the smaller transcripts were generated by splicing events. Evidence was obtained that indicated that each subgenomic RNA species shared a common 5′-splice donor. The 5.0-kb mRNA was found to be expressed at relatively low levels, was difficult to detect consistently, and appeared to be generated by a single splicing event which linked the 5′ exon to the 3′ region of pol. The 4.0-kb transcript was concluded to be the env mRNA on the basis of its hybridization pattern with the various probes and its abundance. The 2-kb species was found to be multiply spliced and was encoded by sequences derived from orf2 but was not detected by probes representing 3′-env/3′-orf sequences. The 1.8-kb species was shown to consist of sequences representing orf1, part of orf2, and the 3′-orf/env and may represent the message for the EIAV trans-activator gene.