47S

47S, in a molecular biology context, refers to the 47S pre-rRNA, the primary transcript produced by RNA polymerase I from ribosomal DNA (rDNA) repeats in the nucleolus. This long precursor contains sequences destined to become the mature ribosomal RNAs—18S, 5.8S, and 28S—arranged with internal transcribed spacers (ITS1 and ITS2) and flanked by external transcribed spacers (5' ETS and 3' ETS). The 47S transcript is the starting point for ribosome biogenesis, a process tightly linked to cell growth and proliferation.

Processing of the 47S pre-rRNA is a multistep maturation pathway. The ETS and ITS regions are removed, and the remaining rRNA sequences are chemically modified by small nucleolar ribonucleoproteins (snoRNPs) that guide methylation and pseudouridylation. The result is the mature 18S rRNA (small subunit) and 5.8S and 28S rRNAs (large subunit), which assemble with ribosomal proteins to form functional ribosomes.

Genetically, rDNA repeats containing the 47S unit are organized in tandem arrays, notably on the short arms of several acrocentric human chromosomes. Copy number varies among individuals and species. Expression of the 47S pre-rRNA is regulated by cellular growth signals and ribosome biogenesis factors, linking transcriptional activity to metabolic state. Dysregulation of 47S transcription or processing is associated with diseases such as cancer and ribosomopathies. In research and diagnostics, 47S pre-rRNA levels serve as a proxy for nucleolar activity and overall protein-synthesis capacity, measured by methods like Northern blot, RT-qPCR, and RNA-FISH.