If this is simply for checking the integrity of your in vitro transcription reaction, you can probably use a high molecular weight DNA ladder in place of an RNA ladder. The single stranded RNA will run much faster than the DNA fragments (theoretically 2x faster), so you be able to estimate the RNA band size using something like GeneRuler 1 kb DNA Ladder or GeneRuler High Range DNA Ladder.

Does it have to be an RNA ladder? I think you would find better luck with a high molecular weight DNA ladder.

Are you able to sequence this and determine the # of bp from those results?

Hi Ricardo Requena Platek ,

Its hard to come by such a commercial ladder as it is really difficult to produce as well as stabilize such long ss molecules in a mixture.

Do give DNA markers a try if you are checking integrity.

On this note did you do an IVT to produce the ~20kb RNA? If yes, may i know the kit you used?

Thanks,

Subham.