Final answer:
The E1A protein of adenovirus is crucial for activating other early genes of the virus by altering host cell transcription mechanisms, which enables efficient viral replication for its lifecycle and is used in gene therapy.
Step-by-step explanation:
The E1A protein of adenovirus plays a crucial role in the activation of other early genes of the virus upon infection. After the adenovirus attaches to a host cell and inserts its DNA, E1A is among the first viral genes expressed. E1A then acts to regulate the expression of other viral genes by interacting with the host cell's transcription machinery. Specifically, E1A binds to cellular transcription factors, such as the retinoblastoma protein (pRb), thus altering cell cycle regulation and enabling the viral genome to be transcribed more effectively.
By doing this, E1A can activate other viral early genes that are necessary for viral replication and the eventual synthesis of late viral genes responsible for assembly and release of new viral particles. This process is critical in the gene therapy where an adenovirus vector is used to deliver and express a functional gene within a human cell with the aim of treating a disease.