The absence of a nuclear envelope in prokaryotes does not prevent the cell from controlling gene expression by modifying RNA after transcription. Prokaryotes do have several mechanisms for controlling gene expression at the RNA level, including RNA editing, RNA stability control, and translation regulation. For example, riboswitches are regulatory RNA sequences that can bind to small molecules and control gene expression by altering the structure of the RNA molecule and affecting its translation. Additionally, CRISPR-Cas systems use RNA-guided nucleases to edit or cleave RNA molecules, providing another mechanism for controlling gene expression in prokaryotes.