Final answer:
Myc is an important immediate early response gene that is involved in the transition from G1 to S phase of the cell cycle and it is quickly expressed following RTK signaling and activation of the MAP kinase pathway.
Step-by-step explanation:
Among the options provided, Myc is an important immediate early response gene that is involved in the transition from the G1 phase to the S phase of the cell cycle. Once RTK signaling, through the MAP kinase pathway, is activated, immediate early response genes like Myc are quickly expressed without requiring new protein synthesis.
Retinoblastoma protein (Rb), while important for regulation at the G1 checkpoint, is not considered an immediate early response gene. Instead, Rb modulates the cell cycle by controlling the progression from G1 to S phase through its interaction with E2F transcription factors, whereas Cyclin D pairs with Cdk4 or Cdk6 to form active kinases that assist in pushing the cell past the G1 checkpoint by phosphorylating Rb, but it is not categorized as an immediate early response gene.