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上传于 2013-10-10 04:44 (219 KB)

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IP: 137.43.20.*   JANEWANGJK55 发表了评论   2013-10-11 04:44
The Col plasmids encode colicins, specific bacteriocidal proteins excreted by strains of E. coli harbouring the corresponding Col plasmid.
These strains are resistant to the colicins they produce because the plasmid also encodes a specific immunity protein but the colicin molecules will kill other strains not harbouring the Col plasmid (Col-) by interfering with one or other of the essential metabolic processes.
                      -------------<<Genetic Elements in Escherichia coli>> by Peter Smith-Keary
IP: 137.43.20.*   JANEWANGJK55 发表了评论   2013-10-11 04:56
The principal F genes and their funcions are:
ori V the origin for vegetative replication.
inc, rep promote replication from oriV.
oriT the origin for transfer replication.
tra ALEKBVCWUNFHG required for pilus formation; traA encodes F-pilin, the major protein sub-unit of the pilus.
traN, traG stabilise the mating pairs of bacteria
tra MYDIZ involved in DNA metabolism during conjugation.
tra I encodes a helicase and tra Y and tra Z act together and promote strand nicking at oriT.
tra S, tra T act to prevent mating between pairs of F+ bacteria.
tra J encodes a protein required to activate transcription of traM and the transfer operon.
finP Fertility inhibition. A regulatory gene; encodes an RNA which, when associated with the finO gene product, prevents expression of traJ. However, the finO gene of F is inacitve as the IS3 element is inserted into it.
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IP: 137.43.20.*   JANEWANGJK55 发表了评论   2013-10-11 05:01
The F plasmid is assembled from 3 componets; the transfer region which encoedes the F pilus and transfer functions, the insertion sequence region adn the replication region.

The transfer functions are only expressed if a functional traJ gene is present - this encodes a protein which activates the transcription of both traM and the tra operon. Note that there are 4 promoters in this region and that finP and traJ are transcribed in opposite directions and that their transcripts overlap at their 5' ends.
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IP: 137.43.23.*   JANEWANGJK55 发表了评论   2013-10-15 05:01
oriT  is the origin of conjugative transfer in the F plasmid, where the DNA is nicked and a single strand of plasmid DNA begins to transfer from the donor to the recipient.
oriT  is a 463- nucleotide segment immediately upstream of traM.

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