RNA:protein ratio of the unicellular organism as a characteristic of phosphorous and nitrogen stoichiometry and of the cellular requirement of ribosomes for protein synthesis Reportar como inadecuado




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BMC Biology

, 4:30

First Online: 05 September 2006Received: 12 March 2006Accepted: 05 September 2006

Abstract

BackgroundMean phosphorous:nitrogen P:N ratios and relationships of P:N ratios with the growth rate of organisms indicate a surprising similarity among and within microbial species, plants, and insect herbivores. To reveal the cellular mechanisms underling this similarity, the macromolecular composition of seven microorganisms and the effect of specific growth rate SGR on RNA:protein ratio, the number of ribosomes, and peptide elongation rate PER were analyzed under different conditions of exponential growth.

ResultsIt was found that P:N ratios calculated from RNA and protein contents in these particular organisms were in the same range as the mean ratios reported for diverse organisms and had similar positive relationships with growth rate, consistent with the growth-rate hypothesis. The efficiency of protein synthesis in microorganisms is estimated as the number of active ribosomes required for the incorporation of one amino acid into the synthesized protein. This parameter is calculated as the SGR:PER ratio. Experimental and theoretical evidence indicated that the requirement of ribosomes for protein synthesis is proportional to the RNA:protein ratio. The constant of proportionality had the same values for all organisms, and was derived mechanistically from the characteristics of the protein-synthesis machinery of the cell the number of nucleotides per ribosome, the average masses of nucleotides and amino acids, the fraction of ribosomal RNA in the total RNA, and the fraction of active ribosomes. Impairment of the growth conditions decreased the RNA:protein ratio and increased the overall efficiency of protein synthesis in the microorganisms.

ConclusionOur results suggest that the decrease in RNA:protein and estimated P:N ratios with decrease in the growth rate of the microorganism is a consequence of an increased overall efficiency of protein synthesis in the cell resulting from activation of the general stress response and increased transcription of cellular maintenance genes at the expense of growth related genes. The strong link between P:N stoichiometry, RNA:protein ratio, ribosomal requirement for protein synthesis, and growth rate of microorganisms indicated by the study could be used to characterize the N and P economy of complex ecosystems such as soils and the oceans.

AbbreviationsGRH Growth rate hypothesis

SGR Specific growth rates

SGR max Maximum SGR of the organism in the study

RGR Relative growth rate calculated as SGR divided by SGRmax

PER Peptide chain elongation rate

m RNA Mass of total RNA

m Pr Mass of proteins

P Total mass of phosphorous per cell

N Total mass of proteins per cell

m rRNA Mass of ribosomal RNA per cell

F Ra Fraction of active ribosomes

n aa Cellular protein content in amino acids equivalents

n R Number of ribosomes per cell

F rRNA Fraction of ribosomal RNA in total RNA calculated as the ratio mrRNA and mRNA

N a Avogadro-s constant

M nucl Average mass of nucleotide

n nuclR Number of nucleotides per ribosome

M aa Average mass of amino acid

Electronic supplementary materialThe online version of this article doi:10.1186-1741-7007-4-30 contains supplementary material, which is available to authorized users.

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Autor: Tatiana V Karpinets - Duncan J Greenwood - Carl E Sams - John T Ammons

Fuente: https://link.springer.com/article/10.1186/1741-7007-4-30



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