recent crystal structure of yeast TBP/TATA-Box Complex

[WILLARD at MVAX.WISTAR.UPENN.EDU]

In the recent crystal structure referenced above (Nature, 365, p. 512) the
protein DNA complex is crystallized under the following conditions:

Hanging drop contains:	0.25 mM protein; 0.5 mM DNA; 15% PEG 8000; 
			20 mM BTP pH 7.5; 3.75% Glycerol; 1% ethylene glycol;
			500 mM NaCl or KCl

equilibrated over
resevoir containing: 	30% PEG 8000; 40 mM BTP pH 7.5; 2.5% glycerol;
			2% ethylene glycol; and 500 mM NaCl or KCl.

My question is twofold.  First, what effect do glycerol and/or ethylene glycol
			have on stability/co-crystallization of protein/DNA
			complexes?

			Second, why is the concentration of glycerol actually
			1.5x HIGHER in the drop than in the resevoir, whereas
			ethylene glycol is (as usually is the case) half the
			concentration in the drop than in the resevoir?

Any reply to either this newsgroup or to me personally would be appreciated.

Thanks.

Rob Willard
WILLARD at WISTB.WISTAR.UPENN.EDU

The Wistar Institute/University of Pennsylvania Chemistry Department