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18 Cards in this Set
- Front
- Back
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Cell with a _____ makes a special sex pilus. The sex pilus
enables the donor cell to make contact with the recipient cell. |
- F-factor
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Explain conjugation in terms of ssDNA vs dsDNA
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- F factor plasmid is sent as a ssDNA --> plasmid recircularizes in recipient --> F DNA becomes dsDNA in the donor & recipient
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About 20 genes in the ______ are required for the F transfer to take place.
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- tra operon
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What kind of genes are in the tra operon?
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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 |
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oriT
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- "cis" acting sequence that is site of nicking so that ssDNA can be transferred
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TraJ
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- positive regulator protein of tra operon
- without it you cannot express the tra operon |
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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
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-tra
- sex pilus - ori T site |
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But what if there is a non-conjugative plasmid in the donor cell as well? Will that transfer at high frequency?
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- no will not transfer the non-conjugative plasmid
- will only transfer pConj plasmid |
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What if in the donor cell there is also a non-conjugative plasmid with an oriT site? Will that transfer at high frequency?
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- 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 |
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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
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- constitutively (100% of time)
- repressor |
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R factor is very closely related to F factor, but what do they make?
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- has a tra repressor --> turns of Tra J --> not wasting energy & not sticking out pilus to infect everyone
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just after transfer of R plasmid the sex pilus is built (aka tra genes not repressed), why?
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- 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 |
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why does F plasmid express pilus constitutively?
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- because a long time ago an insertion mutation occured in the repressor gene
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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?
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- 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 |
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Hfr strain
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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 |
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why is it called Hfr strain?
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- because can transfer genes close to F factor sequences on bacterial chromosome with high frequency to F- cells
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What are 3 ways that F can excise from the chromosome?
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1) regenerate F
2) generating F'lac 3) generating defective F'lac |
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What is F'lac?
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- 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 |
