6. The Ti plasmid of Agrobacterium tumefaciens is a self-transmissible plasmid t
ID: 73565 • Letter: 6
Question
6. The Ti plasmid of Agrobacterium tumefaciens is a self-transmissible plasmid that can be conjugated to some plants. How could you create a mobilizable plasmid that can also be conjugated to plants?
7. You are working with two different, naturally mobilizable plasmids that one can be conjugated along with an unrelated self-transmissible plasmid, but the other cannot. What do you think likely accounts for the difference?
8. You notice that null mutations that inactivate PriA or RecA cause slight but similar decreases in growth of cultures of both mutants. Why is this unexpected?
Explanation / Answer
6 Ans:
Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. conjugation is a mechanism of horizontal gene transfer as are transformation and transduction although these two other mechanisms do not involve cell-to-cell contact.
Bacterial conjugation is often regarded as the bacterial equivalent of sexual reproduction or mating since it involves the exchange of genetic material. During conjugation the donor cell provides a conjugative or mobilizable genetic element that is most often a plasmid or transposon. Most conjugative plasmids have systems ensuring that the recipient cell does not already contain a similar element.
The genetic information transferred is often beneficial to the recipient. Benefits may include antibiotic resistance, xenobiotic tolerance or the ability to use new metabolites. Such beneficial plasmids may be considered bacterial endosymbionts.
7 Ans:
working with two different, naturally mobilizable plasmids that one can be conjugated along with an unrelated self-transmissible plasmid, but the other cannot, because for the process of conjugation that Fertility F-plasmids, which contain tra genes. They are capable of conjugation and result in the expression of sex pilli. So, other plasmid would not contain tra genes. They are not capable of conjugation.
8Ans:
priA null mutants grow slowly and are prone to acquire mutations that suppress the slow growth phenotype. In order to measure the viability of priA mutants, while limiting cell propagation to ensure the absence of suppressor mutations, we used pAM-priA, a plasmid that replicates only in the presence of IPTG and carries the priA wild-type gene. Propagation of pAM-priA containing cells in the presence of IPTG allows plasmid maintenance and expression of the plasmid-encoded PriA protein. In the absence of IPTG, the pAM-priA plasmid stops replicating and cell division leads to the formation of plasmid less cells.
Inactivation of homologous recombination is responsible for the beneficial effect of the recA mutation as inactivation of only the SOS response by a lexA (Ind). mutation did not improve the viability of priA recO and priA recO recF mutants These results indicate that RecA-catalysed recombination events are detrimental in priA recF OR cells. In contrast with recA inactivation, recD inactivation slightly decreased the viability of priA recF and decreased that of priA recO mutant 50-fold, indicating a requirement for DNA degradation initiated at DNA double strand ends.
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