Final answer:
Antisense RNAs are regulatory non-coding RNAs transcribed from the opposite DNA strand of the mRNA, playing a role in RNA interference by binding to and preventing mRNA translation.
Step-by-step explanation:
Regulatory RNAs that are transcribed from the opposite DNA strand to that of the mRNA are called antisense RNAs. Antisense RNAs are non-coding RNA molecules that play a crucial role in the process of RNA interference (RNAi). In this process, antisense RNAs, which can include small interfering RNAs (siRNAs), bind to complementary sequences of mRNA, preventing the mRNA from being translated into proteins. This regulatory mechanism is used by cells to control gene expression and protect against viral infections.