Over the past few years, evidence has been accumulating to indicate that ribosomal subunits are not simply tape-heads that decode mRNA sequences into polypeptide chains, but that they also play an active role in regulating the expression of some mRNAs via specific interactions. In mammals, the 18S rRNA of 40S ribosomal subunits is a key component in mediating these interactions. Our development of a synthetic 18S rRNA expression system enables systematic analysis of this ribosomal component. This talk will review this exciting new field, discuss how modulation of rRNA is being used for analysis of natural ribosomal function, and explore how this approach opens up possibilities for modifying and extending ribosomal function. Learning Objectives: 1. Define basic principles of mRNA translation 2. Classify different mechanisms of translation regulation