Messenger RNA of infectious pancreatic necrosis virus is polycistronic.

Abstract

Infectious pancreatic necrosis virus (IPNV) is an economically important fish pathogen. The virus particles contain two large segments of double-stranded (ds)RNA1–4, which encode four different intracellular primary gene products5,6. The smaller genome segment (‘B’) encodes the largest of these four proteins and the larger genome segment (‘A’) encodes the other three by a mechanism which does not seem to involve post-transla-tional cleavage of a large precursor polypeptide in vivo7. Previous results8,9 have indicated that only two species of mRNA are produced, one from each genome segment8, and that one of these viral mRNAs (that produced from segment B; ref. 7) is monocistronic. The other mRNA, which is transcribed from segment A (ref. 7), encodes three proteins, which may be produced by a mechanism involving multiple initiation and termination sites for translation, rather than post-translational cleavage5–7. To distinguish between these two possible mechanisms, we have studied the translation in vitro of the denatured IPNV genomic dsRNA segments. We report here that the mRNA transcribed from genome segment A is polycistronic.