Sijo.A

B.Sc.Botany & Biotechnology

Mar Ivanios College,Tvm,Kerala

India

An expression vector is a plasmid or virus designed for gene expression in cells.

Expression is depends on the collection of sequence that is surrounded around a gene that can be recognised by the bacterium.

These sequences provide instructions for transcription and translation process.

The three important sequence for E.coli genes are as follows.

1. Promoter region

2. Ribosome binding site

3. Terminator region

They are the upstream elements that codes for RNA.

It is the site of interaction with RNA polymerase before making RNA.

It gives location and direction to start transcription.

The ribosomal binding site on mRNA is called Shine Dalgarno Sequence.

It was discovered by Shine and Dalgarno.

It is purine (G,C) rich sequence.

It helps in the positioning of ribosome correctly with initiation code.

It is the region that tells the RNA polymerase to stop making RNA from DNA template.

The terminator sequence usually a pallindrome sequence that forms a stem loop hair pin structure that leads to the dissociation of RNA polymerase from DNA template.

Genes of higher organism is also surrounded by expression signals.

But their nucleotide sequence are not same as in that of E.coli.

If the foreign gene is inactive in E.coli simply because the bacterium does not recognise its expression signals.

A solution of this problem is that insertion of foreign gene into a vector.

The expression vectors provides signals and foreign gene is transcribed and translated.

Eg: PET series of vectors: PET 28, PET 32