During development, yfg expression is regulated by proteins E, F and G, which are abundant and have long half-lives. After a specific stage of development, protein E is activated by a single short wave of phosphorylation. This leads to the following events:
1. Phosphorylated E activates F
2. Active F activates G
3. Active G promotes yfg expression
4. Active F completely inhibits E, and active G completely inhibits F function
Which one of the following describes the expression of yfg soon after the “specific stage of development” is reached?

Correct option is B

Correct Answer:
(b) One pulse of transcription
Explanation:
The system described forms a negative feedback cascade.
A transient activation of E triggers sequential activation of F and G, leading to yfg expression.
However, once F becomes active, it shuts off E, and once G is active, it shuts off F, terminating further signaling.
Because E is activated only briefly and the downstream inhibitors are long-lived, yfg expression occurs as a single transient pulse.
Information Booster :
· Pulse generation is common in developmental gene regulatory networks.
· Negative feedback loops convert transient signals into defined expression bursts.
· Long protein half-lives help stabilize the termination of signaling.
· Such circuits ensure precise temporal control of gene expression.
Additional Information (Incorrect Options):
(a) Continuously transcribing: Ruled out due to strong negative feedback on E and F.
(c) Transcription not initiated: Incorrect since G does become active briefly.
(d) Multiple pulses: Requires repeated activation of E, which does not occur here.