What is the key functional characteristic of the core molecular clock mechanism identified in flies?

A self-sustaining oscillation created by a loop where gene products turn off their own production.

The fundamental breakthrough in chronobiology was identifying the molecular mechanism that maintains the 24-hour rhythm without constant external prompting; this mechanism is self-sustaining. This persistence is achieved through a feedback loop established by the clock genes and their protein products, such as the PER protein in flies. Once synthesized, these gene products interact with the transcription machinery to inhibit or block the transcription of the very genes that created them. This action effectively turns off their own production, creating a molecular trough. As the inhibitory proteins degrade over time, the inhibition is lifted, allowing production to resume, thereby establishing a measurable, self-perpetuating oscillation that defines the cycle length.