Phosphorylated p53 is a protein that accumulates in the nuclei of cells that have damaged DNA where it functions to block the cell cycle and activate DNA repair. The p53 gene that encodes this protein is an example of a (n):

a. tumor suppressor gene.

b. protein kinase.

c. proto-oncogene.

d. oncogene.

Tumor suppressor gene.

Explanation:

p53 gene is an important gene that codes for the proteins involve in the regulation of the cell cycle. p53 gene is also known as teh genome guardian or the gate keeper.

p53 gene acts as the tumor suppressor gene as the recessive mutation in this gene leads to the development of tumor. This gene suppress the tumor activity and normally regulate the process of the cell cycle. This gene also prevents the gene mutation.

Thus, the correct answer is option (a).