FIGURE 1 Chemical modification of rRNA inactivates the 30S ribosomal subunit. The graph shows the percentage of normal activity (synthesis of polypeptide) over time. In the absence of kethoxal (squares), the 30S subunit retained activity; in the presence of kethoxal (circles), activity was impaired over time. A control reaction lacking tRNA and mRNA had virtually no activity (triangles). The chemical structure of a kethoxal-