I have been transforming my BL21 cells with my recombinant plasmid, however I never get any colonies in blue-white screening. I use ampicillin for selection. Most of the time for blue-white screening, I would observe faint blue patches, not colonies, on my plates, even on the controls.
After restriction digestion, the DNA would be positive on agarose gel, but after ligation, I digest them again to verify on agarose gel but I wouldn't get any bands. Could it be the competent cells or the ligation problem? I have tried using 1:1, 1:3, 1:5 and 1:10 ratios.