what is an integron? - recinto universitario de...
Post on 08-May-2020
10 Views
Preview:
TRANSCRIPT
1
Transferencia Lateral (Horizontal)
de Genes y su Impacto en la
Diversidad Bacteriana
Carlos M. Rodríguez Minguela, Ph.D.
Departamento de Biología
cmrodriguez@uprm.edu
Ext. 3933
What is an integron?
• bacterial gene capture and expression system
• may encode traits that confer selective
advantages
• these may include but are not limited to:
1.antibiotic resistance
3.metabolic genes
2.virulence factors
4.restriction enzymes
2
beta-lactamase
P(int)
P(c)
aminoglycoside
modifying enzymetrimethoprim resistant
dihydrofolate reductase
59-be 59-be 59-be59-be
Structure and function of integrons
integrase
mRNApolycistronic
P(int)
integrase
•excision of captured genes
Function of integrons:
3
P(int)
integrase
•exchange of captured genes among different
integron classes
Function of integrons:
P(int)
integrase
Function of integrons:
•reassortment of captured genes
4
beta-lactamase
P(int)
P(c)
aminoglycoside
modifying enzymetrimethoprim resistant
dihydrofolate reductase
59-be 59-be 59-be59-be
Function of integrons
• as reservoirs of cryptic genes
truncated
mRNA
imperfect palindromes (2o structure)
• not expressed
• could be transferred
Function of integrons
• as sources of species genome diversity
E. coli cell A E. coli cell B
Inactivaton of Intl gene:
• results in the fixation of
captured genes
integron
absent
• prevents insertion, rearrangement,
and exicision of genes
5
Classification
of
integrons
Two major groups:
1. Mobile integrons (resistance integrons):
• physically linked to mobile DNA elements:
1.transposons 2.conjugative
transposons
3.conjugative
plasmids
• prevalent in clinical strains
• may confer resistance against 9 different antibiotics
6
Two major groups:
2. Superintegrons (chromosomal integrons):
• large numbers of inserted gene cassettes
• not associated with mobile DNA elements
All integrons are grouped into classes
according to the ID% of the integrase
amino acid sequence.
1
5’ 3’
5’ 3’
3’
intl3 attl3 blaiIMP-1 attlC ?
5’
Class1
Class 2
Class 3
40%
a.a. ID
61%
a.a. ID
1
Classic resistance (mobile) integrons)
a.a.=amino acid
7
- Integrons are not mobile by themselves.
- they are mobilized by transposons and
conjugative plasmids.
Secuencias de Inserción y Transposones
- elementos genéticos que se mueven
de una molécula de DNA a otra
-pueden moverse de un lugar a otro en un
cromosoma o de un cromosoma a un plásmido
8
Secuencias de Inserción y Trasnposones
Secuencias de inserción Transposones
IR
IRIR
IRIRIR
IRIR IR IR
IRIR
•transposón más simple
•tnp: gen de transposasa
reconoce corta y liga DNA durante
transposición
•IR: inverted repeats, punto de
contacto de la transposasa
•se componen de dos secuencias
de inserción
•poseen genes adicionales a la
tnp (transposasa)
Transposición
tnp
tnp
tnp
9
Transposons: segments of DNA
capable of jumping from one
DNA molecule into another,
or of moving around to
different positions in the
genome of a single cell.Target DNA Target DNA Target DNA Target DNA IRIR tnp IRIR IRIR tnp IRIRABR gene
Donor DNA IRIR tnp IRIRDonor DNA
Target DNA Target DNA Target DNA ABR gene
Composite transposon
TranspositionTransposition
IS element IS element
Donor DNA IRIR tnp IRIRDonor DNA
Transposition into new target DNA (plasmid, chromosomal)
Transposase
Donor DNA D Donor DNA IRIR tnp IRIR IRIR tnp IRIRABR geneDonor DNA D Donor DNA IRIR tnp IRIR IRIR tnp IRIRABR gene
IS = Insertion Sequence (insertion elements
are the smallest transposons, they
combine to form composite transposons)
IR = inverted repeat, identical
DNA sequences reading in opposite directions
(DNA is double stranded) these are targeted by the transposase
and are compatible with the recipient DNA region
tnp = transposase, transposon
encoded enzyme that excises
the transposon from a donor
DNA molecule and inserts it
into a recipient DNA molecule
Horizontal Gene Transfer
of Antibiotic Resistance
Traits
transposase
integron
integron
integron
tn
tn
tntn
tn
tn
Chromosome
Bacteriophage
Transposon
“Free” DNA
Plasmid
Plasmid
Chromosome
tn
tn
tn
10
65% de las diferencias genéticas entre los genomas completos de 70 bacterias
relacionadas se debieron a la presencia de elementos genéticos transmitidos
lateralmente
• genomas de bacteriofagos insertados
• transposones
• secuencias de inserción
Published articles using next generation
high throughput sequencing technology
11
Nature 437, 376-380 (15 September 2005)
• novel fibre-optic slide of individual wells
and is able to sequence 25 million bases,
at 99% or better accuracy, in one four-hour run
• 100-fold increase in throughput over
current Sanger sequencing technology
• shotgun sequencing and de novo assembly
of the Mycoplasma genitalium genome with
96% coverage at 99.96% accuracy in one run
of the machine
Beijing Genomics Institute
- reversible terminator-based sequencing chemistry
≥600 Mb/day, using as little as 100 ng to 1ug starting material
12
ABI-SOLiD
Output: 6 gigabases
of mappable data.
DNA sequencing
by ligation.
¿Como pueden identificarse
genes que han sido
transferidos horizontalmente?
13
• análisis comparativo de genomas
Bioinformática: análisis computacional de secuencias de DNA y proteínas
¿Como pueden identificarse genes que han sido transferidos horizontalmente?
Observaciones que Sugieren Transferencia Lateral de Genes
características atípicas en la secuencia de
un gen en relación con el resto del genoma.
• G+C %
• tendencias en el uso de codones
• presencia de secuencias repetitivas
flanqueando el gen sospechoso
¿Como pueden identificarse genes que han sido transferidos horizontalmente?
14
2. características atípicas en la secuencia de un gen en relación con el resto del
genoma (diferencias en G+C % )
¿Como pueden identificarse genes que han sido transferidos horizontalmente?
= 65% G+C
= 48% G+C
características atípicas en la secuencia de un gen en relación con el resto del
genoma (tendencias diferentes en el uso de codones )
¿Como pueden identificarse genes que han sido transferidos horizontalmente?
Pro = CCG
Arg = CGT
= 65% G+C
= 48% G+C
Pro = CCT
Arg = AGA
15
top related