““Second, the production of RNA Messages was coordinately regulated. When the sugar source was switched to lactose, the bacteria turned on an entire module of genes-several lactose-metabolizing genes-to digest lactose. One of the genes in the module specified a "transporter protein" that allowed lactose to enter the bacterial cell. Another gene encoded an enzyme that was needed to break down lactose into parts. Yet another specified an enzyme to break those chemical parts into subparts. Surprisingly, all the genes dedicated to a particular metabolic pathway were physically present next to each other on the bacterial chromosome-like library books stacked by subject-and they were induced simultaneously in cells. The metabolic alteration produced a profound genetic alteration in a cell. It wasn't just a cutlery switch; the whole dinner service was altered in a single swoop. A functional circuit of genes was switched on and off, as if operated by a common spool or a master switch. Monod called one such gene module an operon. The genesis of proteins was thus perfectly synchronized with the requirements of the environment: supply the correct sugar, and a set of sugar-metabolizing genes would be turned on together.””
