Plasmid question

[tittu]

Which of the following is just a cloning plasmid and not an expression plasmid?
pBAD 18- Cam
pBCSK
pUC 18
pET

This came in a medical college entrance exam i gave.
Iv'e lookedit up later, and found pET, pBAD and PUC are surely expression systems.
However, though listed under cloning vectors in stratagene website, pBCSK has T7 and T3 promoters, and hence can be used to express proteins!
Is my argumentwrong or is the question flawed?

[blcr11]

pUC18 is not an expression vector. It is used for cloning. It has a lac promoter for the expression of lacZ, but not a T7 (or such) promoter for specific expression of cloned sequences. In the absence of an insert, colonies are blue when grown on IPTG/X-gal plates. Cloning into the MCS site disrupts the lacZ gene which results in white/colorless colonies on IPTG/X-gal. This blue/white screening is a quick way to distinguish plasmids with inserts from plasmids without. You have to subclone your insert into another vector for expression. I'm not familiar with pBCSK, but pET and pBAD are definitely expression vectors. If pBCSK has a T7 promoter then most likely it is an expression vector also.

[tittu]

pBCSK, a phagemid has the T7 promotor in the MCS. I am uploading its map here. Would this alter your response?

Please check this out

[blcr11]

pBC-SK can be used for expression. It might not be the easiest to use, but it is possible.