DNA ligation help

[kostya levay]

Here are my 2 cents:

Once I had very bad experience in cloning 12kb insert into Bluescript 
with transformation into DH5a. Actually, all of purified plasmids 
contained deletion of different size. Then I realised that the 
products of leaking promotors? could be harmful for bacteria and lead 
me into troubles. Interestingly, that DH5a doesn't have "lacIq" in its 
genotype, i.e. overproduction of lac repressor protein, inhibiting 
transcription from the lac promoter. Many other cells do have lacIq.
I transformed my ligation into JM101, got my construct from the first 
hit and since then DH5a is on my black list (when I have tricky 
situations). 

Cheers,

Kostya Levay
Plant Pathology
U.of Kentucky, Lexington.