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ANAT 214 Lecture Notes - Orf 2, Endonuclease, Antimicrobial Resistance

Anatomy & Cell Biology
Course Code
ANAT 214
Louis Hermo

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Lecture 23-26 for problem set 8
Lecture 37 is question and answer session
Discovery of transposable elements
Eukaryotic transposable elements (insertion vs ..)
Prokaryotic tranpsoable elements
Genetics and the detection of the eunexpected- corn
Barbara mcClintock discover there’s chromosome breakage
She did cytochron genetics
She discovered that there’s a locus where you get chromosome breakage and
called it dissociator
Rare unstable alleles
Affect tonly a single gene distal to usual breakage point
Suggested that Ds (dissociator) is mobile but only in the presence of Ac
They couldn’t map Ac so it seemed to be mobile
Ccrosses of wild isolate males and lab strain females
F1 progeny are sterile
Unstable mutation of white from dysgenic cross remicent.. (?)
…Enlarged mutant allele in E coli
Unstable lac and gal
Found to contain extra DNA
They take lamda phage (which can take up host genome.. a good vector)
containing wild type gel+ and do that w/ unstable allele, they found that they
have two populationso f DNA size.
For gel + they find low density DNA..less DNA
Gel- had higher density…more DNA
So mutation in gel is caused by insertion of extra DNA
Bacterial insertion sequences
Hybridization experiment for gal insertion mutants found that same sequence
over and over again
In other parts of the bacterial chromosome too
Encodes transpoase protein which performs transposition
Terminal inverted repeats (required for transposition)
Target site duplication (created during insertion!!)
[insert pic of the
Bacterial transposons
Composite (ex: Tn9): Bacterial genes flanked by 2 insertion sequences.
Cannot or can move by itself
Dependening on transposn. Both Is’ could move on own
OR one IS may be disabled and transposon depends on the intact IS
Transposable element vs. transposon
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Transposon can move on its own or they flank a gene and carry that
gene with them (all together called transposable element)
No insertion sequences
Flanked by inverted repeats
Encoded transposase
Mechanisms of transposition
Conservative (do not duplicate….cut and paste) into new location
Ex: Tn10
Medated by transposases
Cuts at target site
Cuts out from old site (w/ flanking region)
Insert into new site
Host repairs cut sites to generate target site duplication..
Replicative (copy and paste)
Mediated by transposase
Cut at target
Recombination and cointegrate
Instead of cutting out of old site, it ligate into the new site
Resaluase (a protein that’s involved)
No need to know the detail of mechanism
Medical consequences of bacterial transposons
Multiresistance plasmids (passing genes between bacteria)
Can do
Transposition into plasmid
Recombination between IS
Can easy pass between bacteria by conjugation through sex pili
Not limited by species
Which statements about composite transposons is false?
They are composed fo two insertion sequences flanking a passenger gene
The flanking insertion sequences are often defective
True, that’s why they often carry other genes with them
They are composed fo two insertion sequences flanking a transposase
IS have their own transposases.. so false
The passenger gene si often an antibiotic resistance gene
They are flanked in the genome by direct repeats (target site duplication)
Eukaryotic transposable elements
Class1: retrotrasnposons (need reverse transposase)
LTR: long terminal repeat
LINES: long interspersed elements
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