Ribosomal RNA synthesis

Ribosomal RNA synthesis" is not a specific molecule or protein, but refers to the **biological process** by which ribosomal RNA (rRNA) is transcribed from ribosomal DNA (rDNA) primarily by RNA polymerase I (Pol I) in the nucleolus (except for 5S rRNA, which is transcribed by RNA polymerase III)[1][4][5][6]. This process is the first and rate-limiting step in ribosome biogenesis, ultimately controlling the cell's capacity to synthesize proteins[1][2][4]. Ribosomal RNA synthesis is highly regulated and involves various assembly and processing factors to ensure accurate folding, modification, and maturation of the rRNA molecules[2][1]. Disruption or dysregulation of ribosomal RNA synthesis is implicated in disease, particularly cancer, as cancer cells rely on increased ribosome biogenesis for rapid growth[5]. While some cytotoxic drugs (e.g., Actinomycin D) target this process, "ribosomal RNA synthesis" itself is not a single protein, receptor, or enzyme, but a multi-component transcriptional process; thus, it does not fit the canonical therapeutic target classification. **Caveat:** This entry is “incorrect” as a target because a biological process (ribosomal RNA synthesis) should not be considered a molecular drug target by standard nomenclature; instead, the appropriate targets are enzymes or factors mediating this process, such as "RNA polymerase I" or individual rRNA processing factors[1][4][5][6].

Inhibition of RNA polymerase I (by Actinomycin D and similar agents)