Ribosomal RNA is the RNA that combines with specific proteins to form ribosomes, the sites for protein synthesis.  On the ribosome, the mRNA and tRNA molecules interact to translate information transcribed from the gene in to specific protein molecule.

Ribosomes: A ribosome is a cytoplasmic nucleoprotein structure that acts as the machinery for the synthesis of proteins from the mRNA templates. The mammalian ribosome contains two major nucleoprotein subunits, a larger one (60S) and a smaller one (40S).

The 60S subunit contains a 5S ribosomal RNA (rRNA), a 5.8S rRNA, and a 28S rRNA. There are also probably more then 50 specific polypeptides. The smaller 40S subunit contains a single 18S rRNA and approximately 30 polypeptide chains.

The highly methylated ribosomal RNA molecules are packaged in the nucleolus with the specific ribosomal proteins.  In the cytoplasm, the ribosomes remain quite stable and capable of many translation cycles.

The functions of the ribosomal RNA molecules in the ribosomal particle are not fully understood, but they are necessary for ribobinding of mRNA to ribosome and its translation.