Question

Transposon mutagenesis lab. pRL27 strain. Serratia Marcescens used. LB-DAP, LB-KAN plates were used.

Describe the mutation created in this exercise (at the DNA level), and explain why it is relatively stable and does not revert back to producing normal amounts of red pigment?

Answer 1

The mutation created in this exercise is a polar mutation by making use of transposon in the experiment.Transposons have the advantage of disrupting gene expression.Transposons can truncate the gene product, cause polar mutation, stops RNA transcription from rho-independent transcriptional terminators and can also drive expression of genes near insertion site. Polar mutation results in the loss of expression of other genes which are within the operon of that gene (downstream of insertion site).
The mutation is stable since the transposase gene producing enzyme enabling transposon movement is not a part of the transposon region/ transposable element on the plasmid pRL27. Therefore, the movement of transposon after its first insertion is hindered and the mutation becomes stable. This is the reason why the mutation does not revert back to producing colonies with normal amounts of red pigments. The stable mutation results in production of mutant colonies which appear white. These white colonies are transposants in which he transposon has jumped into the pigment protein generating gene and disrupted the expression of pigment producing mRNA.