Beschreibung:
<jats:title>Significance</jats:title>
<jats:p>It has been known for decades that purified small subunits of the ribosome can interconvert between active and inactive conformations in experiments performed under simplified conditions, but the physiological relevance of this switch has remained unclear. We probed the structure of ribosomal RNA in healthy living cells and discovered that stably assembled 30S subunits exist predominantly in the inactive conformation, with structural differences localized in the functionally important decoding region. Disrupting the ability to interconvert between active and inactive conformations compromised translation in cells. In-cell RNA structure probing supports a model in which “inactive” 30S subunits comprise an abundant in-cell state that regulates ribosome function.</jats:p>