Amount of DNA to send for sequencing - linear response in signal intenstiy? - (Apr/26/2011 )

Hi,

I recently sent samples to an establishment for sequencing. I sent the maximum concentration of DNA that was advised for the sample type (500 ng; plasmid, miniprep). My sequences all came back with weak signals (generally 100-200 signal intensity). I sent the samples again, this time increasing the DNA concentration beyond the advised concentration. Where I sent twice the amount of DNA, signal intensity increased five-fold and a three-fold increase in DNA gave a nine-fold increase in signal. Is that non-linear response normal, or should I try sequencing elsewhere?

BTW, the DNA was quantified both on the NanoDrop and by densitometry, against a size-marker (the densitometry gave somewhat higher values - the NanoDrop values were used to calculate DNA to be sent).

it's been my experience, with the beckman coulter ceq-8000 and dtcs chemistry, that the effect of increasing or decreasing template will have a non-linear effect on the signal strength of the sequencing product.