DNA Repair and Recombination

What does mismatch repair fix?

Base-base mismatches and small insertion/deletion loops from replication errors

What proteins are involved in bacterial mismatch repair?

MutS, MutL, MutH

What marks the parental strand in E. coli mismatch repair?

Methylation of adenine in GATC sequence

What proteins are involved in human mismatch repair?

MSH (MutS homologs), MLH/PMS (MutL homologs)

What disease is caused by defective mismatch repair in humans? *

HNPCC (Hereditary Nonpolyposis Colorectal Cancer)

What does base excision repair fix?

Small, non-distorting lesions: deaminated, depurinated, methylated bases

What enzyme removes the damaged base in Base Excision Repair?

DNA glycosylase

What enzyme cuts the 5’ phosphodiester bond at the AP site in Base Excision Repair?

AP endonuclease

What enzyme fills the gap in Base Excision Repair?

DNA polymerase

What enzyme seals the nick in Base Excision Repair?

DNA ligase

What does nucleotide excision repair fix?

Bulky, helix-distorting lesions like pyrimidine dimers and chemical adducts

What proteins recognize damage in NER? (you get XP for recognizing damage)

XP proteins (humans), Uvr proteins (E. coli)

What enzyme excises the damaged strand in NER?

Excinuclease at 5’ and 3’

What disease is caused by defective Nuclear Excision Repair?

Xeroderma Pigmentosum 

What is deamination?

Conversion of cytosine to uracil or adenine to hypoxanthine

What does UV radiation cause?

Pyrimidine dimers (cyclobutane rings between adjacent thymines)

What is the consequence of pyrimidine dimers?

Block replication and transcription

What is a clinical consequence of transposition?

Spread of antibiotic resistance genes in bacteria

How does HIV integrate into the genome?

Through a transposition-like mechanism

What enzyme removes the sugar by cutting the 3’ phosphodiester bond in Base Excision Repair?

AP Lyase