Transcription of structural genes by RNA polymerase to produce messenger RNAs (mRNAs) and the translation of such messengers by polyribosomes to produce proteins are intimately coupled processes in bacterial cells (1). In fact, it is possible to reconstruct coupled transcription and translation systems in vitro from separated bacterial components (2,3). Using techniques developed by Miller and Beatty (4) to prepare the nuclear contents of amphibian oocytes for electron microscopy, we can now directly visualize genetically active bacterial chromosomes. In these studies, we have identified both structural genes and ribosomal RNA (rRNA) genes (5,6).