A central aim of cell biology was to understand the strategy of gene expression in response to the environment. Here, we study gene expression response to metabolic challenges in exponentially growing Escherichia coli using mass spectrometry. Despite enormous complexity in the details of the underlying regulatory network, we find that the proteome partitions into several coarse-grained sectors, with each sector's total mass abundance exhibiting positive or negative linear relations with the growth rate. The growth rate-dependent components of the proteome fractions comprise about half of the proteome by mass, and their mutual dependencies can be characterized by a simple flux model involving only two effective parameters. The success and apparent generality of this model arises from tight coordination between proteome partition and metabolism, suggesting a principle for resource allocation in proteome economy of the cell. This strategy of global gene regulation should serve as a basis for future studies on gene expression and constructing synthetic biological circuits. Coarse graining may be an effective approach to derive predictive phenomenological models for other ‘omics’ studies.

Although the objective of any ‘omic science is broad measurement of its constituents, such coverage has been challenging in metabolomics because the metabolome is comprised of a chemically diverse set of small molecules with variable physical properties. While extensive studies have been performed to identify metabolite isolation and separation methods, these strategies introduce bias toward lipophilic or water-soluble metabolites depending on whether reversed-phase (RP) or hydrophilic interaction liquid chromatography (HILIC) is used respectively. Here we extend our consideration of metabolome isolation and separation procedures to integrate RPLC/MS and HILIC/MS profiling. An aminopropyl-based HILIC/MS method was optimized on the basis of mobile-phase additives and pH, followed by evaluation of reproducibility. When applied to the untargeted study of perturbed bacterial metabolomes, the HILIC method enabled the accurate assessment of key, dysregulated metabolites in central carbon pathways (e.g., amino acids, organic acids, phosphorylated sugars, energy currency metabolites), which could not be retained by RPLC. To demonstrate the value of the integrative approach, bacterial cells, human plasma, and cancer cells were analyzed by combined RPLC/HILIC separation coupled to ESI positive/negative MS detection. The combined approach resulted in the observation of metabolites associated with lipid and central carbon metabolism from a single biological extract, using 80 % organic solvent (ACN:MeOH:H2O 2:2:1). It enabled the detection of more than 30,000 features from each sample type, with the highest number of uniquely detected features by RPLC in ESI positive mode and by HILIC in ESI negative mode. Therefore, we conclude that when time and sample are limited, the maximum amount of biological information related to lipid and central carbon metabolism can be acquired by combining RPLC ESI positive and HILIC ESI negative mode analysis.

The relation for the compressibility of hard convex bodies (Boublik, 1975) is combined with the power series in (u/k T) and (V°/V) (Alder et al., 1972) to obtain the most general and accurate equation of state of fluids. 24 universal constants of the series were fitted to the internal energy and PVT data for argon. The equation also contains 5 characteristic constants that were fitted to the properties of 11 fluids to show its validity at all densities ranging from zero (second virial coefficients) to the liquid density at T/Tc = 0.55 that corresponds to the triple point of argon. The interaction energy u/k appears to be equal to the critical temperature Tc for small molecules but it becomes a function of the temperature for non‐spherical molecules, in agreement with the theory of non‐central forces.

The ribosome is an essential and highly complex biological system in all living cells. A large body of literature is available on the assembly of the ribosome in vitro, but a clear picture of this process inside the cell has yet to emerge. Here, we directly characterized in vivo ribosome assembly intermediates and associated assembly factors from wild-type E. coli cells using a general quantitative mass spectrometry (qMS) approach. The presence of distinct populations of ribosome assembly intermediates was verified using an in vivo stable isotope pulse-labeling approach, and their exact ribosomal protein (r-protein) contents were characterized against an isotopically labeled standard. The model-free clustering analysis of the resultant protein levels for the different ribosomal particles produced four 30S assembly groups that correlate very well with previous in vitro assembly studies of the small ribosomal subunit, and six 50S assembly groups that clearly define an in vivo assembly landscape for the larger ribosomal subunit. In addition, de novo proteomics identified a total of 21 known and potentially new ribosome assembly factors co-localized with various ribosomal particles. These results represent new in vivo assembly maps of the E. coli 30S and 50S subunits, and the general qMS approach should be a solid platform for future studies of ribosome biogenesis across a host of model organisms.

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