Problem with isolation of plasmid after ligation?

i did transformation of a high copy number plasmid in ecoli dh5alpha cell after ligation of my required gene.i got 1 single colony.i tried 2 isolate plasmid from the colony obtained but the quantity is even less than 5ng/ul.since it was a double digestion product(gene)doubt on colony is nt of mch help.what should i do as im getting pcr confirmation of presence of gene.how should i increase the yield ?can any1 help?Problem with isolation of plasmid after ligation?
The fact you only got one colony suggest the transformation failed. Even thought the PCR worked, this could have been due to contamination.





Possible reasons for failure include:





(a) ligation reaction failed - include a positive control if possible (linearized empty vector)


(b) wrong selection medium - stupid I know, but I've done it before


(c) competent cells are dead - include positive control (plasmid)