DNA transposition

Question 1

what are transposons?

Answer 1

• mobile genetic elements i.e. DNA sequences that carry genes enabling their movement within or between genomes.
  Plasmids, viruses and cassettes or integrones are also MGEs

Question 2

where are transposons found?

Answer 2

in all genomes; bacteria to man.
- can carry antibiotic resistance genes
- cause genome instability and affect gene expression, contribute to genome evolution

Question 3

what is in the structure of a typical bacterial transposon; Tn3

Answer 3

• target site duplication at each end
• transposase
• binding site; where resolvase protein represses transcription of transposase gene and its own gene and where it catalyses resolution by recombination across two copies of Tn3 in a cointegrate
• B-actamase
• left and right inverted repeats (38bps)

Question 4

DNA transposons move by one of two mechanisms

Answer 4

• cut and paste; no increase in copy number
• replicative transposition; goes via cointegrate intermediate producing two copies from one

Question 5

transposons in eukaryotic cells

Answer 5

applied as genetic tools for mutagenesis and gene isolation

Question 6

what are transposons used for?

Answer 6

• identify essential genes
  -introduce transposons on plasmid into cells
• allowit to jump into genome
• grow up cells
• establish location of transposons by PCR
• genes that are never disrupted are essential

Question 7

what did Ig genes and RAF recombinase come from?

Answer 7

a transposon

Question 8

what are retroelements?

Answer 8

• mobile genetic elements
• transpose via an RNA intermediate
• cope and paste mechanism
• require reverse transcriptase (RT) activity
• best known examples ; retroviruses like HIV

Question 9

what are defective retro-elements?

Answer 9

LINES and SINES comprise 30% of human genome.
One million copies of the Alu (SINE) sequence

Question 10

summary on lecture points

Answer 10

• genomes require constant repair
• multiple repair pathways
• link betwen replication, repair and recombin. (transcription)
• DNA, though carrying genetic code, isn’t static; contains movable genetic elements
• highly active scientific field