<s>[INST] context: p53 gene (TP53): Located on the short arm (p) of chromosome 17, p53 gene (also termed TP53 because of molecular weight of 53 KD for the protein) like pRB is inhibitory to cell cycle. However, p53 is normally present in very small amounts and accumulates only after DNA damage. 
The two major functions of p53 in the normal cell cycle are as under: 

In blocking mitotic activity: p53 inhibits the cyclins and CDKs and prevents the cell to enter G1 phase transiently. This breathing time in the cell cycle is utilised by the cell to repair the DNA damage. 
In promoting apoptosis: Normally, p53 acts together with another anti-oncogene, RB gene, and identifies the genes that have damaged DNA which cannot be repaired by inbuilt system. p53 directs such cells to apoptosis by activating apoptosis-inducing BAX gene, and thus bringing the defective cells to an end by apoptosis. This process operates in the cell cycle at G1 and G2 phases before the cell enters the S or M phase.

Because of these significant roles in cell cycle, p53 is called as 'protector of the genome’.
Mohan H. Textbook of pathology. Jaypee Brothers Medical Publishers; 2015. Edition 7. Page 206 [/INST] question: The tumor suppressor gene p53 induces cell arrest at: | options: A: G2-M phase B: S-G2 phase C: G1-S phase D: G0 phase | answer: C </s>