For viruses that contain RNA as coding nucleic acid, the strands are said to be either positive-sense (+ or also called plus-strand) or negative-sense (- or also called minus-strand).
The naming is dependent on whether it is complementary to viral mRNA.
Positive-sense (+) viral RNA is identical to viral mRNA and thus can be immediately translated by the host cell.
Negative-sense (-) viral RNA is complementary to mRNA and must be first converted to positive-sense RNA by an RNA polymerase before translation.
DNA viral strand nomenclature is similar to RNA nomenclature, in that the coding strand for the viral mRNA is complementary to it (-), and the non-coding strand is a copy of it (+).
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