Problems in cDNA library construction

[Helen Mok]

Dear all,

We have constructed a cDNA library with Clontech SMART
cDNA Library Construction Kit. After library
screening, some clones were picked and eluted in SM
buffer. Some were then taken out for PCR (with vector
specific primers) to check the size of the inserts.
However, all clones showed a bright sharp band of
around 200 bp and nothing else. After the conversion
of the phagemid to plasmid, we did the same PCR again,
but this 200 bp band disappeared. 

We are wondering are those empty vector that has been
packaged and propagated.

Have anyone ever encountered this problem? Or does
anybody know what's gone wrong? 

Any suggestions or advice would be appreciated,
thanks!

Helen Mok 



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