The gene product specified by a double stranded RNA in the flax rust (Melampsora lini) is expressed during rust growth.

Strain SP6 of the flax rust (Melampsora lini) contains 11 double-stranded RNAs (dsRNAs) of unknown function. A large open-reading frame (B3ORF1 in dsRNA B3 encodes a polypeptide of 614 amino acids, and using an antiserum raised against the B3ORF1-glutathione S-transferase fusion protein prepared from a bacterial expression system, we have detected the presence of a 67 kDa polypeptide in rust urediospores. This polypeptide, identical in size to that of the predicted translation product of B3ORF1 , was not detected in spores from either a fungal strain lacking the B3 dsRNA or an isogenic strain containing no dsRNA. These data indicate that B3ORF1 present in the flax rust B3 dsRNA is expressed in vivo which warrants farther investigation in search for its function during rust development.