introduction to mismatch repair

what can happen during DNA replication

mismatches between bases

how to fix mismatches

DNA polymerase and DNA MMR proteins

failure to fix mismatches results in

mutations

Lynch syndrome

autosomal dominant

cancerous syndrome

inherited mutation in MMR genes

autosomal dominant

only need one copy to cause syndrome

always occurring no matter what on first 22 chromosome pairs

MMR

mismatch repair

3rd leading cause of cancer death in men and women

colorectal cancer (CRC)

what percent of colon cancers are hereditary

5%

gremlin mutation

inherited

cancers of Lynch syndrome

colon, ovarian, endometrial, urinary tract, stomach, brain, skin, other cancers

high penetrance

shows up very quickly in population with allele

tissue will develop as the defective allele

high penetrance in LS

80% for CRC

60% for endometrial

20% for other cancers

Constitutional Mismatch Repair Deficiency (CMMRD)

siblings of two parents with LS can develop

balletic MMR mutations

cancer spectrum more severe

cancers in CMMRD

50%develop brain tumors

50% digestive tract cancers

33% haematological malignancies

Mismatch recognition complex

MutSalpha

eyes of MMR proteins

MutSalpha

made of two polypeptides: MSH2 and MSH6

1st protein in MMR system

MSH2

apart of MutSalpha

often mutated in LS

MSH6

apart of MutSalpha

often mutated in CMMRD

40% of families with LS were associated with mutations of this

model organism

yeast

why yeast

conserved genes with humans

cost efficient

plasmid

circular DNA molecule

gene on plasmid

MSH6

DNA MMR proteins in eukaryotes

MutSalpha

MutLalpha + PCNA

DNA polymeraseδ

Exol

Rpa

ligase

Mismatch recognition

MutSalpha

what does MutSalpha recruit

MutLalpha

MutLalpha

does strand discrimination

endonuclease cleavage with help of PCNA

DNA polymeraseδ

resynthesizes strand

Exol +Rpa

Mismatch removal by exol

binding of Rpa

ligase

puts DNA strand back together

classification of yeast

eukaryotes

fungi

can exists as haploids or diploids

haploid yeast

16 chromosomes

diplod yeast

32 chromosomes

saccharomyces cerevisiae

budding yeast

microbe

cannot see without microscope

yeast during experiment

should be white

Louis pasteur

role of yeast fermentation

baker’s yeast

sourdough

brewer’s yeast

alcohol, beer

deletion of msh6

msh6(w/triangle)

protein gene symbol

first letter uppercase

Msh6

allele (mutant)

msh6…

wildtype

functional

MSH6

tolerated amino acid change

most likely no effect on MMR function

not tolerated amino acid change

most likely has an effect on MMR function

functional assy

haploid yeast

CAN assay