Message <= 500nt for N. blot?

[Jeffrey Joseph Martino]

I'm posting this for someone without net access.

We're probing for a message which comes out 1 kb and above on
Northern blots of mouse RNA.  We'd like to simultaneously
probe for another RNA which gives a distinct and separate
band, say between 100 and 500 bases, as an internal control.
Something common like a housekeeping gene would be great.

I'd appreciate any and all suggestions.

Thanks very much.