Protein profiles in the presence or absence of 1 mM spermine. The horizontal axis represents the approximate pH range of the isoelectric focusing first dimension, and the vertical axis represents the molecular weight (Mw). The "layered view" superimposes two composite images, each composed from three 2-D gels of independently grown replicate cultures. All E. coli cultures were diluted 500-fold and grown at 37°C to an OD600 of 0.2 in LBK with (pink) or without (green) 1 mM spermine. Culture media were buffered as described under Methods. (A) 100 mM MOPS, pH 7.0. (B) 100 mM TAPS, pH 8.5.