Table 1.

Summary of data for nuclear organelles measured in sucrose solutions

	Volume fraction	Protein concn (g/cm3)	Dry refractive index
Cajal bodies	0.121	0.154	1.57
Speckles	0.134	0.170	1.55
Nucleoli	0.160	0.203	1.55

Column 1 gives the volume fraction occupied by macromolecules in each organelle (slope of OPD/t against refractive index; Figure 7). Column 2 converts this volume fraction to protein concentration on the assumption that each organelle consists entirely of protein with a dry density of 1.27 g/cm³ (Barer and Joseph, 1954). Column 3 gives the refractive index of a solution that would match the refractive index of the dry organelle contents (the x-intercept in Fig. 7).