Lecture 7 Flashcards
How can bacteria with natural antibiotic resistance on chromosones be transferded. Example in real life
by transposn -> jump onto plasmid -< can horizoontally transfer to recipient host cell by conjugation. This is the method used to transfer vancomycin resistance from differen bacteria through RTF
How do certain transposons acting alone work
Tn916 from Enterococcus faecalis can bear transfer genes and can move betweeen bacteira via conjugation withou tbeing integrated into a conjugatied plasmid.
Tn916 cannot replicate autonomously but wil transfer itself from E. faecalis to a number of recipients and integrate into their chormomes carrying tetracycling resistnace
Transposon conjugation is more common in?
Gram possitives
The accumulation of multiple antibiotic resistnace genes may be due to?
Shuffling of genes between bacterial chormosomes, plasmids, transposons and viruses
How does transposon conjugation work
requires excision of the transposon from its host DNA molecule.
Cirtulization transfer of 1 tstrand of the transposon DNA to the recipient (process is unknown, dont know if pili is needed but cell contact is required)
REplication of the transposon DNA in donor and recipeit.
Replciation of the transposon in the donor and recipient => reinsertion into the donor and recipeient
What can transposon conjugation do
transfer to other genera, to both gram positvie and gram negative.
originally thought to tranfer tetracycline, now theres evidence of vancomycin resistnace
What are the 3 mechanisms segemnts of DNA can be exchnawged
- homoglous recombination
- site specific recombination
- transpositon
Whats homologous recombination
pairing of homooglous or closely relarted sequenes
reuiqre endonucleases to nick DNA, recombination proteins, ligases, ATPases, SSB proteins
processs to exchange chormosomal DNA in prokaryotes and eukaryotes
How are F plasmids usually inserterted and excisited from E. coli
By homologus recombination between similar IS elements on the plasmid and chromosone
How do F plasmids integated
- homoglous recombination occurs within the paired IS elemetns during integration of the F plasmid
- Requires recombination enzymes (Rec proteins) of host and often accessory proteins encoded by the plasmid.
- requires nicking of DNA via endonucleases, SSB bidning proteins to keep ssDNA separate, ligase to ligate the DNA.
chromosme becomes 100 kB larger on integrationa and 100 kB smaller onexicison
How is site specific recombiantion carried out
- heteroduplex
- its an important process in the integration of virus genome into bacterial chormsomes
- enzymes involved are usually speicfic for the virus and the host.
- does not involve the Rec protein used in homoglous reomciniantion
- requires integrase enzyme
- requires recombiantion at very short homologus sequence - attachment site - allow 2 DNA molecules to attach together by base pariring.
integrsases comes and catalyzes the integradtion
What does DNA polymerase do?
Fills in the gaps
Waht does DNA liages do
joins the DNA
What about transposiition?
Use enzyme encoded within the transposons (transopases and in some cases resolvase) and host encoded enzymes: DNA polymerase and DNA ligase
Its a recombination event - uses speficif target sites/preseie
No heteroduplex
can be considered site specific recombination in a broad context using target sequence but exact mechanisms are still unclear bc there is still some element of randomness to the integration of transpsons
What is conservative replcation
Cut and paste, nonreplicateive
Transposase - what do they do?
Target sites are unique for the type of transpsone.
Transposase makes ss nick at each strand of target site: staggereted ends. targe sequnec ie characterisc of transposon
transposase makes blunt unt at the end of directed repeats to release integrated transpsoone, there is ciruclatizaiton
transoposnas ligates the transposon with teh target DNA
Ss gaps in target site are filled by host DNA polumerase and host ligase ligates the end -> direct repats
Difference between replicative transposition and conservative replcation
- Requires DNA syntheiss (conservative doesnt, only time its required is to fill in the gaps)
- Requires site specific recombination
- generates copy of transposon at new site and leaves transposon at original site
- requires an enzyme called resolvase in addition to transposase
Whats the impact of transposons
- Genetic variability:
+ change protein coding regions -> non protein coding regions: long or short term effect depending on stbaility of transposon
+ change regulatory sequence of a gene:
change expression of gene and therefore gene product
deltions, reaarnaements
can be used as mutagens to study gene expression
What happens if a transposon loses its ability to jump in eu
detrimental if its in germ line cells.
Difference between fimbirase and sex pili
these are pili involved in adhereane, not involved in DNA transfer
How do transposons make bacterial cells more virulent
source of multiple antibiotic resistance
alter virulence of a bacterial cell by chanign fimbriae, cell wall, cell envoleep, capsule whichc an:
change ability to evade immune system of host,
improve adherance,
reduce phagocytosis by macropahges, reduce the permeability of certain drugs
