Question

What would the most likely phenotype of an E. coli colony containing pUC18 (without an insert fragment) be if the following de novo mutations occurred early in the growth of a single cell into a colony on your plate (assuming plate contains X-gal, IPTG and Amp)? a. A frameshift mutation in the fifth codon lacZ gene in pUC18. b. A loss of the pUC18 plasmid. c. A deletion of bps at positions 19-25 of the ampicillin resistance gene open reading frame.

Answer 1

The pUC18 plasmid is very important tool for genetic engineering. It contains all the necessary sites which make it a suitable vector such as controllable ori site, restriction digestion site, insertion-compatible sequences and selectable marker. Deletion in one or any of these sequences will render it unuseful and in-appropriate for genetic engineering experiments.

According to the information, there occurs a random de novo mutation in the early growth phase of a single cell colony or pure culture of E. coli. Since the culture was in initial growth phase with all ingredients which make it expressible, this mutation might create a framishift mutation in the bacteria. This is because the plasmid is deboid of any gene insert and hence, in order to maintain the genotype and phenotype, a shift in reading frame might exist. This mutation will not change the phenotype or genotype and the plasmid can still be used for genetic manipulation.

Thus, choice A is correct.