Northern blot background dots - (Dec/17/2005 )

Hello
I have been consistently getting lots of small dark dots all over my northern blots. My bands and marker are present, but the little dots make the blot quite ugly. Has anyone seen this before and know how to get rid of it?
Here is some info about my protocol (quite close to the protocol in Current Protocols (Wiley & Sons): Im using Hybond-XL nylon membrane, downward transfer in 20XSSC. My probe is a 22nt DNA oligo, 32-P labeled. I hybridize using an SSC buffer recipe from Current Protocols. Ive tried a few other buffers but still get dots (and sometimes lose the bands).
Cheers!

You may try mixing the probe with some hybridization buffer instead of depositing the concentrated probe in the bottle with membrane. Spots might results from microdroplets that get (electrostatically?) on the membrane.
You do a pre-hybridization, do you?
Good luck.

this is probably a silly suggestion, but do you use old scissors or forceps when handling the membrane? any tiny amount of rust on your membrane will show up as a little black spot at the end...I do not use P-32, so maybe this is different for you, but I have seen it with both Southerns and Westerns; also, with chemi blotting, sometimes you get blotches if you use old reagents and you're getting some precipitation...are either of these things helpful for you?

also, if you are unable to find the problem, maybe try to post a pic for us?

good luck

Hi
Thanks for the suggestions. The dots are gone, I think being careful to add the probe to the buffer first did the trick.
Cheers!