transduction (by infection with a virus: does not require cell to cell contact and is not sensitive to DNase) Transformation occurs in only some bacteria and requires the formation of a receptor/channel complex (Com protiens in Bacillus), one strand is degraded and the other strand undergoes homologous recombination with the host chromosome Conjugation requires a fertility factor (genetic element that encodes genes required for conjugation) that can be present on a plasmid in F+ cells or incorporated into the cost chromosome in Hfr cells During conjugation the donor cell pulls recipient into close contact using cell surface appendages, called pili, a conjugation channel is formed connecting the two bacteria and the donor DNA is cut at the OriT site, DNA replication proceeds by rolling circle mechanism resulting in the transfer of one strand to the recipient cell where the second strand is synthesized Chromosomal genes can be mapped by interrupted mating between Hfr cells and F cells Excision of an F factor from the chromosome of an Hfr cell can in some cases result in the transfer of host chromosomal DNA to the F plasmid, which can be transferred to recipient cells (sexduction)
Transduction can be generalized (in which random bits of host DNA are encapsulated into a page coat anomalously resulting in the inclusion of flanking chromosomal DNA) Transposons Bacteria can harbor cut and paste IS elements or composite elements (in which two closely spaced IS elements transpose together taking intervening sequences with them) IS (insertion sequences) elements have terminal inverted repeats and an intervening sequence that encodes the transposase gene, transposition involves the removal of the IS element from its original site and insertion into a new site by creating a staggered cut followed by insertion and gap filling, which creates a target site duplication
Bacteria can also harbor replicative transposons (Tn3) which transpose by a mechanism that includes fusion of donor and recipient DNA elements followed by transposon replication, homologous recombination and resolution that releases one of the elements resulting in the duplication of the transposon Eukaryotes can harbor cut and paste transposons- Ac/Ds elements in corn and P elements in fruit flies Transpositions of a Ds element requires the presence of an Ac element encoding the transposase gene, which the Ds element lacks Eukaryotes can also harbor retroviruslike elements (Ty1 in yeast) that genetically resemble retroviruses but lack the genes needed to spread outside of the cell, these
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