Natural process of plasmid transfer is called

Natural process of plasmid transfer is called - as rolling...

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Natural process of plasmid transfer is called conjugation . Best understood for the E. coli F (fertility factor) plasmid (about 95 kb in size, 1 to 2 copies per cell). E. coli cells carrying the F plasmid are called " male " and those that do not carry the F plasmid are called " female ". The F plasmid from male cells can be transfered to female cells changing them into male cells . F plasmid contains a tra (transfer) operon with 20 structural genes necessary for conjugation: Donor (male) cells mixed with recipient (female) cells ----- mating pairs form joined by a special structure called conjugation bridge (EM Figure). Conjugation bridge comes about because certain F genes encode proteins that form a specialized tubular extension on the cell surface of a donor cell called pilus that then establishes cell-cell contact with recipient cell. Transfer occurs because the plasmid is able to replicate by a process known
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Unformatted text preview: as rolling circle replication . In this process, one strand of the F plasmid DNA is nicked at a specific sequence [the ori sequence] by a particular endonuclease encoded in the tra operon. Other proteins then bind to the 5' end of the nicked strand and guide that single strand (strand displacement) into the recipient cell (Figure). DNA polymerase can replicate a new daughter strand to replace the displaced strand. Once the displaced DNA strand crosses the conjugation tube and enters the recipient cell, a copy strand is replicated to yield double-stranded DNA which is finally converted into the usual circular and supercoiled form. In the end the original recipient cell is transformed into a donor cell and can now take part in spreading the plasmid....
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This document was uploaded on 11/03/2011 for the course BIOLOGY MCB2010 at Broward College.

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