Final answer:
The suppression of Rb tumor suppressor protein regulates the G1-S transition by monitoring cell size and blocking the production of proteins necessary for the transition. When the cell reaches the appropriate size, Rb is phosphorylated and becomes inactive, allowing the transition to occur.
Step-by-step explanation:
The G1-S transition in the cell cycle can be achieved through the suppression of the Rb tumor suppressor protein. Rb plays a regulatory role by monitoring cell size. In its active state, Rb binds to transcription factors, such as E2F, and blocks the production of proteins necessary for the G1/S transition.
As the cell increases in size, Rb is phosphorylated and becomes inactivated, allowing E2F to activate the gene that produces the transition protein. This mechanism ensures that the cell has reached the appropriate size before progressing to the S phase.