Nuclear run-on assay (contribution of elongation)

[Hetty]

In our course 'analytical molecular biology' (last master year - University of Ghent) some techniques are described. Amongst them the nuclear run-on assay. In the course the professor gave a remark but we (the students) can't make anything of it. Maybe some of you can?

First he described the nuclear run-on assay and then he says (i'm just copying it):
Remark: by comparing a run-on with a DNA-probe corresponding to the 5' end, and a run-on assay with a DNA-probe corresponding to the 3' end of the gene, one can get an idea whether there is also an involvement of regulation of elongetion.

E.g. stimulus/control
5' probe 2x
3' probe 20x
conclusion: important contribution of elongation

He didn't explain it is his lesson and the above text is all there is written. Anyone?

Thanks in advance!