Reeta yadav. roll no. 01. transposable elements in prokaryotes
1.
2. Introduction
Mechanisms of transposition
Bacterial transposons
IS elements
Composite transposons
Non-composite transposons
Medical significance of bacterial
transposons
Conclusion
References
3. Transposable elements are also known as
“TRANSPOSONS” , “JUMPING GENES” ,
“MOBILE GENETIC ELEMENTS”.
A DNA sequence that can change its position
within the genome, sometimes creating or
reversing mutations and altering the cells genome
size.
Term was given by “Hedges and Jacob(1947).
Barbara McClintock’s discovery of these
jumping genes, through an analysis of genetic
instability in Maize, earn her noble prize in 1983.
7. simplest bacterial transposons (small DNA
fragment).
first detected in certain lac(-) gene mutations of
E. coli (it reverses the wild type phenotype).
compactly organized (~2500 bp) and contain
only genes whose products are involved in
transposition.
Inverted terminal repeats are found at the ends.
Some IS elements encode transposase, an
enzyme.
8.
9. These are Cut &
Paste
transposons.
Two different
way to cut DNA
by
restriction
enzymes:
-blunt ends
-over hanging
ends -(sticky
ends)
10. bacterial chromosome & plasmids may contain IS
elements.
Conjugative R plasmids have spread multiple
drug resistance in bacterial populations.
11. bacterial cut-and-
paste transposons
--denoted by the
symbol Tn.
--are created when
two IS elements insert
near each other.
Have two IS
elements flanking
a region that
contains one or
more genes for
antibiotic
resistance.
12.
13. don’t have IS elements at each of their ends.
larger than the IS elements
contain genes that are not required for
transposition
14. Tn3 is a
replicative
transposon that
transposes by
temporarily
fusing DNA
molecules into a
cointegrate
when the
cointegrate is
resolved, each of
the constituent
DNA molecules
emerges with a
copy of Tn3
15. Many bacterial transposons carry genes for
antibiotic resistance.
It is relatively simple matter for these genes to
move from one DNA molecule to another- for
instance, from a chromosome to a plasmid. This
genetic flux has a profound medical significance
because many of the DNA molecules that acquire
resistance genes can be passed on to other cells.
This process has occurred in several species
pathogenic to humans, including strains of
Staphylococcus, Neisseria, Sbigella & Salmonella.
Many bacterial infections causing diseases such
as dysentery, tuberculosis, & gonorrhea are
difficult to treat.
16. The spread of multiple drug resistamnce in bacterial
populations has been accelerated by evolution of
conjugative R plasmids that carry the resistance
genes .
These plasmids have two components- one called
the resistance transfer factor , or RTF, contains the
genes for conjugative transfer between cells, the
other, called the R-determent, contains the genes for
antibiotic resistance.
These can be passed from one species to another,
even between quite dissimilar cell types-for e.g
between a coccus and a bacillus.
Thus, once multiple drug resistance has evolved in a
part of the microbial kingdom, it can spread to other
parts with relative ease.
17. Snustad, D.Peter & Simmons J.Michael.2003. Principles
Of Genetics(2nd edition) John Wiley & Sons. Newyork.
page no. 441-446.
Weaver , F Robert & Hedrick W.Philip .1997. Genetics(3rd
edition). Wm.C.Publishers. page no. 354-365
Web links:-
http://www.nature.com/scitable/topicpage/transposons-the-
jumping-genes-518
http://www.ndsu.edu/pubweb/~mcclean/plsc431/transelem/t
rans5.htm
http://bio.classes.ucsc.edu/bio105l/EXERCISES/F%20TRA
NSFER/Tn.pdf
