Table 1. Concentrations and properties of expressed fluorescent proteins.

	mCherry-U2AF35	mEGFP-U2AF65	mEGFP-U2B″
Concentration in splicing (μM)	0.2	1.3	1.4
% labeled:unlabeled on RNA aff. purifn.	75:25	69:31	49:51
Molecules bleaching in 2 versus 1 steps, −ATP	33:189*	33:243*	39:162
Molecules bleaching in 2 versus 1 steps, +ATP	21:218*	25:186*	30:252

Concentrations were calculated from western blotting of nuclear extract alongside recombinant protein; the percentages labeled or unlabeled (endogenous) recovered after affinity purification on biotinylated RNA were also calculated by western blotting; the numbers of molecules recorded as bleaching in one or two steps in the absence of exogenous RNA are shown. *, done in the presence of ribonuclease.