Question

what was the purpose of transforming cells from URA3- minus to URA3+ plus?

Answer 1

Ura is uracil.

It is required by the cells to synthesise RNA. The cells used in transformation experiment in laboratory cannot synthesise uracil on their own.

Whenever we are transforming a vector with a foreign gene, then in the foreign gene we also insert a gene for selectable marker. This marker helps us to differentiate between transformed and non transformed cells. Commonly used selectable markers are resistance to antibiotics, blue white screening, herbicide resistance etc.

Uracil in cell s is also a selectable marker. Normally cells cannot synthesise uracil and whenever they are grown, uracil is added in the media. But when we use these cells for transformation experiments, then along with the foreign gene, we also insert in them the gene encoding uracil synthesis so that these organisms can now synthesise uracil.

In the end when the transformation is completed, we can select for transformed cells. Cells which have taken up the foreign gene will grow in the medium which does not contain uracil and therefore all the cells will be transformed. Non transformed cells will not grow because they do not have gene encoding for uracil.

Hence the use of uracil is a that of a selectable marker.

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