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18 Cards in this Set

  • Front
  • Back
Cell with a _____ makes a special sex pilus. The sex pilus
enables the donor cell to make contact with the recipient cell.
- F-factor
Explain conjugation in terms of ssDNA vs dsDNA
- F factor plasmid is sent as a ssDNA --> plasmid recircularizes in recipient --> F DNA becomes dsDNA in the donor & recipient
About 20 genes in the ______ are required for the F transfer to take place.
- tra operon
What kind of genes are in the tra operon?
1) pilin & pilus assembly
2) nicking & transfer
3) surface exclusion - convert outer membrane in surface of donor cell into situation that is not appropriate for it to engage in conjugation with another F+ cell
- "cis" acting sequence that is site of nicking so that ssDNA can be transferred
- positive regulator protein of tra operon

- without it you cannot express the tra operon
A conjugative plasmid can transfer itself into a different cell, because it carries a___ operon encoding the _____, the DNA transfer apparatus, and the enzyme to nick at the _____ site, the point where transfer begins, then ssDNA plasmid (transferable element) is transferred to recipient cell

- sex pilus

- ori T site
But what if there is a non-conjugative plasmid in the donor cell as well? Will that transfer at high frequency?
- no will not transfer the non-conjugative plasmid

- will only transfer pConj plasmid
What if in the donor cell there is also a non-conjugative plasmid with an oriT site? Will that transfer at high frequency?
- pConj & pNC can be transferred

- either or both can be transferred

- if pNG is transferred alone - it will not become a donor cell b/c doesn't have pConj
The tra operon of F is expressed _______. Most conjugal plasmids have a ______ of the tra operon so that only 1 in 10,000 cells express the pilus genes
- constitutively (100% of time)

- repressor
R factor is very closely related to F factor, but what do they make?
- has a tra repressor --> turns of Tra J --> not wasting energy & not sticking out pilus to infect everyone
just after transfer of R plasmid the sex pilus is built (aka tra genes not repressed), why?
- just after transfer, new donor hasn't yet expressed enough repressor to inhibit TraJ synthesis

- TraJ & tra genes expressed & sex pilus is built

- as time goes on repressor builds up & represses TraJ --> end up with cell that has high repressor level high enough to shut off TraJ & tra operon no longer expressed - no pious
why does F plasmid express pilus constitutively?
- because a long time ago an insertion mutation occured in the repressor gene
what are special genetic elements of F? What are they important for? What happens if sequences same as bacterial chromosome one? What is end result?
- 2x IS3
- 1x IS2
- 1x Tn1000

- exclusively devoted to interaction b/w F factor & other replicons in the cell - aka bacterial chromosome

- homologous recombination - done by RecA

- end result is Hfr strain - cells where conjugative plasmid become part of chromosome
Hfr strain
These are cells in which the conjugative plasmid has become part of the chromosome

- have all genes needed for conjugation, but instead of transferring just plasmid DNA - can also transfer chromosomal DNA

- usually can only transfer portions of chromosome b/c it is too much for them
why is it called Hfr strain?
- because can transfer genes close to F factor sequences on bacterial chromosome with high frequency to F- cells
What are 3 ways that F can excise from the chromosome?
1) regenerate F

2) generating F'lac

3) generating defective F'lac
What is F'lac?
- fertility properties transferred by 100% of donor cells

- lac genes transferred to 100% of donor cells

- other chromosomal genes transferred at low frequency

- all require RecA in donor cell