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BackgroundCell growth rate reflects an organism’s physiological state and largely relies on the ability of gene expression to respond to the environment. The relationship between cellular growth rate and gene expression remains unknown.ResultsGrowth rate-coordinated changes in gene expression were discovered by analyzing exponentially growing Escherichia coli cells cultured under multiple defined environments, in which osmotic pressure, temperature and starvation status were varied. Gene expression analyses showed that all 3,740 genes in the genome could be simply divided into three clusters (C1, C2 and C3), which were accompanied by a generic trend in the growth rate that was coordinated with transcriptional changes. The direction of transcriptional change in C1 indicated environmental specificity, whereas those in C2 and C3 were correlated negatively and positively with growth rates, respectively. The three clusters exhibited differentiated gene functions and gene regulation task division.ConclusionsWe identified three gene clusters, exhibiting differential gene functions and distinct directions in their correlations with growth rates. Reverses in the direction of the growth rate correlated transcriptional changes and the distinguished duties of the three clusters indicated how transcriptome homeostasis is maintained to balance the total expression cost for sustaining life in new habitats.

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Heptamethyl cobyrinate perchlorate, [Cob(II)ester]ClO4, was prepared in a good yield from cyanocobalamin. This hydrophobic complex is structurally comparable to the base-off form of vitamin B12r. Thermodynamic parameters (ΔG, ΔH, and ΔS) for axial ligation of [Cob(II)ester]ClO4 with various amines in dichloromethane and toluene were determined by electronic spectroscopy. The isoequilibrium temperatures obtained from plots of ΔH  vs. ΔS were 194±20 and 317±20 K in dichloromethane and toluene, respectively. The equilibrium is primarily controlled by entropy at ordinary temperatures and the logK1 value varies sensitively along with the change in pKa of amine in dichloromethane, while the equilibrium values were almost invariant to the choice of amine in toluene because the measurements were carried out near the isoequilibrium temperature. The logK1 value for [Cob(II)ester]ClO4, different from the case of cobalt(II)-porphyrin complexes, depends on the nature of solvent used and undergoes wide variations. The possible functions of equatorial ligands involved in these two different complexes in the axial ligation behavior were discussed.

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