Question

If we are cloning a cDNA into a plasmid simply for sequencing purposes, the vector does NOT need to have

Select one:

a. a selectable marker

b. a promoter

c. an origin of replication

d. a restriction enzyme site

e. a primer binding site

Answer 1

Ans:- b. a promoter

Explanation:-

Option a:- A selectable maker enables us to select successfully cloned copies of the plasmid marker.

Option b:- A promoter helps in the transcription of the gene like switching it on or off depending on the requirement of the cell. we don't need this for the said purpose. As only cloning and sequencing of the gene is desired (required purpose) not its expression or transcription (first step of gene expression).

Option c:- Origin of replication is needed to get multiple copies of cloned cDNA in a suitable host.

Option d:- Restriction enzyme site helps in the cloning of specific DNA fragments as it provides a suitable site.

Option e:- Primer binding site is used by vector primers to determine the terminal sequence of the cDNA insert at the 5′ and 3′ ends producing ESTs (Expressed Sequence Tags). These ESTs are used for gene-sequencing.