Yes, it should be fine to store at -20.

I tend to store mine at 4degC after i've performed the heat inactivation. Not sure if there is any cause for concern though unless someone has information to suggest that this reduces the identification of positive clones.

Thanks guys for all your comments.

This is directly from Roche´s RapidLigase protocol "he ligation reaction mixture can be used directly for the transformation of competent cells, or can be stored without heat inactivation at -15 to -25°C."

http://www.rpgroup.caltech.edu/courses/aph162/2006/Protocols/RocheRapidDNALigation.pdf

Go on, it s just DNA, worked for me many times!

It worked with me at -20 for more than one year without any precautions

Yes it is safe, It also worked for me. Just keep on -20 degree

It worked for me too :) and i am really glad, because after three weeks of constant struggle I think iv managed with my cloning (although i am yet to verify). today morning i got to see my colonies finally!!