Direction of Translation in Bacteriophage S13

Suppressible (amber- type) mutants in gene IIIa of bacteriophage S13 show polarity in reducing the activity of only the neighboring gene IIIb. The polarity implies that the genome is translated in the direction of IIIa to IIIb. From the known homology of the messenger RNA with the single-stranded DNA, the orientation of the DNA with respect to the genetic map can also be inferred.