IIRC RNA is made up mostly of the same nucleic acids as DNA. T (something something) is replaced by Uracil. The main difference is that DNA is double stranded whereas RNA is single stranded. Since mRNA uses three acids to represent one of the amino acids that make up the proteins it encodes, and there is a finite amount of amino acids, this means no new proteins are encoded if you add more "letters" to DNA/RNA.

Possibly the RNA could have some secondary function in the folding of the protein or as a complex inside it...

Edit: spelling