Final answer:
Mutant p53 proteins can act as dominant-negative mutants, interfering with the tumor-suppressing functions of normal p53 and contributing to cancer development.
Step-by-step explanation:
The statement that mutant p53 proteins act as dominant-negative mutants is true. Normally, p53 is a tumor suppressor protein that halts cell cycle progression, initiates DNA repair, or triggers cell death in the case of unrepairable DNA damage. However, when mutations occur in the TP53 gene, the resultant mutant proteins can interfere with the function of any remaining normal p53 protein, exerting a dominant-negative effect, rather than being simply recessive. This can prevent the cell from properly responding to DNA damage, leading to unregulated cell division and potentially to cancer. For instance, individuals with Li-Fraumeni syndrome have at least one mutated p53 allele and a significantly increased risk of developing cancer.