Electron micrograph showing transcription of ribosomal RNA genes.

Electron micrograph showing transcription of ribosomal RNA (rRNA) genes in the developing egg cell of the spotted newt. Fibers extending in clusters are molecules of rRNA used in the construction of cell’s ribosomes. The long filaments indicated by green arrow are DNA molecules coated with proteins. RNA molecules get longer as transcription proceeds to completion as indicated by the red arrow. (Courtesy of Oak Ridge National Laboratory , U.S. Department of Energy. Used with permission.)