Figure 2.

Schematic representation of the minimum genetic requirements for adjacent genes that are transcribed independently and those transcribed together as a single operon. Cases 1, 2 and 3 depict instances where gene A and gene B are transcribed independently as distinct transcriptional units, while Case 4 depicts genes organized into a common operon. The minimum requirement for genes of a common operon is only a RBS, while Case 3 emphasizes the numerous genetic elements required if gene A and gene B are organized into separate transcription units.