DNA Recombination Flashcards
3 types of recombination?
- Homologous recombo
- Site-spec recombo
- Transposition
Best known examples of site-spec recombo?
- integration of bacteriophage DNA into bacterial genomes
Define transposition
Movement of genes laterally b/w locations w/i a genome
Practical examples of transposition? (2)
- Antibiotic resistance
2. Drivers of evolution
Does homologous recombo repair DNA lesion?
No, it just synth DNA strand beyond lesion so that replication is not stalled
Main mechanism of homologous recombo repair of DNA lesion?
Reverse branch migration
Major mechanism of homologous recombo repair of SS nicks in DNA?
Homologous recombo b/w leading and lagging strand that allows lagging strand to fill in
What is loss of heterozygosity (LOH)?
- loss of a wild type allele from a heterzyg cell
- loss of functional allele –> cancer formation
2 mechanisms of LOH?
- Mis-segregation (non-disjunction) can lead to segregation of 2 mutant chromosomes and 1 wild type into 1 cell and just 1 wild type into other cell –> one cell dies and the other one could cause cancer
- Homologous recombo can –> a cell that is either homozyg WT or homozyg mutant
2 examples of viral genome integrations in humans mediated by site-spec recombo?
- HTLV virus
2. T-cell lymphoma
What proportion of human genome is made of transposable mobile elements?
~44%
What are retrotransposons? 3 examples?
- transpose by replicative (copy) transposition
- copy of transposon is made and integrates elsewhere in genome
- LINEs (Long Interspersed Nuclear Elements)
- SINEs (most abundant seq in human genome)
- LTRs (Retroviral/Long Terminal Repeat-like transposons)
Importance of Alu family of retrotransposons?
- primate specific
- useful for human/primate evolutionary studies
How to DNA transposons transpose?
Conservative transposition (cut and paste)
Examples of descendants of DNA transposons in humans? (3)
- RAG1/2 recombinase proteins that create antibody diversity
- CENP-E (major centromere binding protein E)
3 components of light chain of Ig’s?
- Variable domain
- Joining domain
- Constant domain
Mechanism of transposition excision of Ig light chain? (3)
- excision recombo occurs after variable domain and before joining domain
- transc of all variable domains and subsequent joining domains + constant domain
- splicing removes unnecessary variable and joining domains
Why does V-J recombo occur?
There are recombo signal seq’s (RSS) b/w every Var and Join domain
Diseases caused by exon shuffling b/w Alu elements?
- hemophilia, from disruption of clotting factor IX
- Duchenne MD, from disruption of Dystrophin
- both are from X-linked genes
Mechanism of Chronic Myelogenous Leukemia (CML)? (4)
- chromo translocation that –> Philadelphia chromo (part of 9 and 22)
- gene fusion b/w Abl kinase locus (ABL – 9) and breakpt. cluster region (BCR – 22)
- expression of chimeric bcr-abl fusion oncoprotein
- const active kinase –> signaling for abnormal growth in myeloid cell lineage
Mechanism of Imatinib tx? (3)
- binds active site of Abl kinase domain of fusion protein in CML
- inhibits substrare phosph
- very lethal to CML cells
Role of ML in bloodstream and tissues? (3)
- Myelobasts (immature leukemic granulocytes) replace bone marrow
- blasts circulate in blood –> hepatosplenomegaly
- % of blasts in blood determines severity (<10% = chronic; >20% = acute)
What is a blast crisis? (3)
- AML
- Sx of tiredness, fever, splenomegaly
- assoc w/ secondary mutations (p53, pRb)
Chromosome translocations implicated in Burkitt (B-cell) lymphoma form of non-Hodgkin’s lymphoma? (3)
- 8 and 14: c-Myc transc factor (proto-oncogene – 8) and heavy chain Ig expression regulatory element (14)
- 8 and 22: c-Myc and lambda chain Ig expression regulatory element (22)
- 8 and 2: c-Myc and kappa chain Ig expression regulatory element (2)
- inappropriately elevated c-myc expression in B-cells –> cell proliferation
