A 27-year-old man has undergone a routine colonoscopy because of his concern over a family history of colon cancer. There is no family history of any other types of cancer. During the colonoscopy a single 2-cm polyp is seen and removed. Histological examination of the polyp shows a villous adenoma. Metaphase chromosomal spread shows microsatellite instability but no translocations or deletions. This patient has most likely inherited a defect that has led to interference in which of the following processes?

Question

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The presence of microsatellite instability suggests a defect in the DNA mismatch repair system, which is often associated with hereditary nonpolyposis colorectal cancer (HNPCC or Lynch syndrome).  DNA mismatch involves a series of enzymes that recognize and repair erroneous insertions, deletions, and misincorporation of bases that can arise during DNA replication and recombination, as well as repairing some forms of DNA damage. Microsatellite instability refers to a condition of genetic hypermutability that results from impaired DNA mismatch repair mechanisms.

A 27-Year-Old Man Has Undergone a Routine Colonoscopy Because of His