Positive-sense RNA

Positive-sense RNA has the sequence orientation of a corresponding messenger RNA, rather than being its complementary template. In a positive-sense RNA virus, the entering genome can provide a coding message for translation, allowing production of the viral machinery that subsequently copies RNA. This is a sequence-and-function distinction, not a claim about the molecule's electric charge.

For example, a positive-sense coding segment $5^{\prime }\text{-AUGGCU-}{3}^{\prime }$ begins with the codons AUG and GCU in that reading frame. Its complementary negative-sense template is $3^{\prime }\text{-UACCGA-}{5}^{\prime }$. A polymerase copying that template produces the positive-sense sequence. Both directions and complementary bases are needed; reversing a string alone is insufficient.

Early experiments with poliovirus made the informational role of viral RNA concrete. Isolated RNA introduced under suitable conditions infected human cell monolayers and yielded virus of the original type. Ribonuclease abolished the isolated RNA's infectivity, whereas intact-virus infectivity resisted the same enzyme treatment, supporting the interpretation that exposed RNA carried the infectious genetic information.^[ref]

This does not mean naked RNA naturally enters every cell efficiently; the experiment depended on preparation and exposure conditions. It also does not eliminate the need for an RNA-dependent RNA polymerase during genome replication. The distinction from Negative-sense RNA concerns how the initial coding message is obtained, rather than whether replication ever requires a complementary strand.