IPTG induction in non E.coli strains

[newsnet customer]

>>IPTG binds to lac repressor coded from lacI, but pUC18 doesn't carry any 
>>lacI gene, so I suppose that lacI is coded from the host strains. Does it?

IPTG binds to the lac z operon to induce the lac z gene to express 
beta-galactosidase. beta-galactosidase hydrolyses colorless X-gal to produce 
insoluble blue preciptate (blue colonies). pUC18 does not have lacI gene as 
this would inhibit the expression of beta-galactosidase, therefore blue 
white screening would be impossible. For the same reason, the host strain is 
a modified strain that also does contain the lacI gene.

>>I've a plasmid, based on pUC18, and trying expression in a strain of 
>>Pseudomonas. IPTG induction doesn't work. Could it be because it lacks of
>>lacI genes in its chromosome?

There are papers on PUBMED that shows that blue white screening is possible 
with Pseudomonas. I assume you did a positive control to check IPTG/Xgal is 
working?

ST