Protein Level Function Research Articles

Structure and Dynamics of the Bacterial Chromosome in E. coli

The bacterial cell's ability to control the topology of a long DNA in the confined environment of the cell is quite remarkable. Despite a great number of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of bacterial chromosomes is minimal, partly because their dynamics have been difficult to observe directly. To visualize bacterial chromosome conformation within living cells, we have developed a bacterial strain containing fluorescent gfp-fusion versions of a chromosome folding protein, Fis, under inducible control. Bacterial chromosomes have been studied in cells and removed from cells, in order to establish their spatial organization and mechanical properties, and to study how those properties are changed by varied external conditions. Space-time studies of the nucleoid in live E coli cells shows a relation between chromosome segregation and cell division under different growth conditions, and it also shows how domain structure and overall conformation of chromosomes vary during rapid and slow growth. In order to study the bacterial chromosome outside of the cell, we have developed methods for isolation of single bacterial chromosomes and directly examining nucleoid mechanical properties as a function of protein levels using micromanipulation methods.

Structure and Dynamics of the Bacterial Chromosome in E. Coli Monitored by Gfp-Fis

The bacterial cell's ability to control the topology of the 1.5 mm-long DNA in the confined environment of the cell is quite remarkable. Despite a great number of studies on bacteria, and especially E coli, our understanding of the spatio-temporal organization of bacterial chromosomes is minimal, partly because their dynamics have been difficult to observe directly. Using fluorescent-protein techniques we can visualize bacterial chromosome conformation during cell growth and division through fluorescent microscopy. We have developed a bacterial strain containing fluorescent gfp-fusion versions of a chromosome folding protein, Fis, under inducible control. Bacterial chromosomes have been studied in cells and removed from cells, in order to establish their spatial organization and mechanical properties, and to study how those properties are changed by varied external conditions. Space-time studies of the nucleoid in live E coli cells shows how domain structure and overall conformation of chromosomes vary during rapid and slow growth, and it also shows a relation between chromosome segregation and cell division under these different growth conditions. In order to study the bacterial chromosome outside of the cell, we have developed methods for isolation of single bacterial chromosomes and our further objective will be to directly examine nucleoid mechanical properties as a function of protein levels using micromanipulation methods.

Nível de proteína bruta para codornas de corte durante o período de crescimento

Estudou-se a exigência de proteína bruta de codornas de corte na fase de crescimento. Foram utilizadas 288 codornas européias EV2, de ambos os sexos em delineamento experimental inteiramente ao acaso, cujos tratamentos consistiram de dietas com seis níveis de proteína bruta (23, 25, 27, 29, 31 e 33%) e quatro repetições de doze codornas por unidade experimental. Estudaram-se o ganho de peso (g), peso corporal ao final de cada período (g), consumo alimentar (g) e conversão alimentar (g/g) do nascimento ao 21ºe do nascimento ao 42º dia de idade. No 42º dia de idade, foram aleatoriamente amostradas e abatidas quatro aves por unidade experimental (dois machos e duas fêmeas), para registro dos pesos e respectivos rendimentos das carcaças, cortes nobres (coxas e peito), vísceras comestíveis (fígado, moela e coração) e gordura abdominal. Do nascimento ao 21º dia de idade, houve efeito quadrático dos níveis de proteína da dieta sobre peso corporal, ganho de peso e consumo alimentar, com pontos de máximo em 30,64, 30,65 e 29,02%, respectivamente. A conversão alimentar durante este período apresentou resposta linear, ao nível de proteína bruta da dieta. Houve efeito quadrático dos níveis de proteína bruta da dieta sobre o peso no 42º dia de idade, com máximo desempenho em 29,93%. Para o ganho de peso houve resposta linear aos níveis de proteína. Houve efeito quadrático no ganho de peso e no consumo alimentar do nascimento ao 42º dia de idade, com os pontos de máximo estimados em 29,81 e 29,11%, respectivamente. O peso corporal antes do abate, o de carcaça e o de peito foram influenciados linearmente pelos níveis de proteína bruta da dieta. Houve interação significativa nível protéico versus sexo. As fêmeas apresentaram resposta linear de rendimento de peito em relação aos níveis protéicos da dieta, enquanto o rendimento do peito dos machos não foi influenciado pela proteína da dieta. Peso corporal, rendimento de peito e peso e rendimento de fígado das fêmeas foram maiores que os dos machos. As exigências de proteína bruta estimada para o máximo ganho de peso de machos e fêmeas de codornas de corte, do nascimento ao 21º e do nascimento ao 42º dia de idade são 30,65% e 29,81%, respectivamente. A exigência para pesos de carcaça e peito é de 33,0% de proteína bruta da dieta.

Optimality and evolutionary tuning of the expression level of a protein

Different proteins have different expression levels. It is unclear to what extent these expression levels are optimized to their environment. Evolutionary theories suggest that protein expression levels maximize fitness, but the fitness as a function of protein level has seldom been directly measured. To address this, we studied the lac system of Escherichia coli, which allows the cell to use the sugar lactose for growth. We experimentally measured the growth burden due to production and maintenance of the Lac proteins (cost), as well as the growth advantage (benefit) conferred by the Lac proteins when lactose is present. The fitness function, given by the difference between the benefit and the cost, predicts that for each lactose environment there exists an optimal Lac expression level that maximizes growth rate. We then performed serial dilution evolution experiments at different lactose concentrations. In a few hundred generations, cells evolved to reach the predicted optimal expression levels. Thus, protein expression from the lac operon seems to be a solution of a cost-benefit optimization problem, and can be rapidly tuned by evolution to function optimally in new environments.

UV band fluorescence ( in vivo) and its implications for the remote assessment of nitrogen supply in vegetation

When excited at 280 nm, intact vegetation produced two overlapping broadband fluorescence emissions; the first centered near 335 nm [ultraviolet` (UV) band], and the second centered near 440 urn (blue band). Separation of these two fluorescence bands was achieved by an iterative nonlinear curve fit procedure utilizing the asymmetric double sigmoidal spectral function. The subsequent ratio of the deconvoluted curve intensities exhibited a significant relation between protein concentration and fluorescence. UV band fluorescence from vegetation treated with varying levels of nitrogen fertilization decreased relative to the blue fluorescence as a function of protein levels. These studies indicate that in vivo UV band fluorescence can be utilized as a nondestructive tool to remotely sense variations in protein concentration due to nitrogen supply. Strong similarities were noted in the UV band fluorescence characteristics of intact vegetation to both membrane-bound and soluble plant proteins containing aromatic amino acids. Pure ribulose 1,5-bisphosphate carboxylase in aqueous solution exhibited UV fluorescence characteristics with excitation and emission distributions similar to those of intact vegetation. Because of its high concentration (up to 70% of the soluble leaf proteins), we believe this protein contributes to the UV band fluorescence emanating from the intact leaf. In addition, similar fluorescence characteristics were observed for two other prominent enzymatic plant proteins; namely, adenosine 5′-tri-phosphatase and carboxylase phosphoenolpyruvate carboxylase. These results indicate that UV band fluorescence emanating from the intact leaf could originate from several plant proteins that contain aromatic amino acids.

Thermal gelation of meat batters as a function of type and level of fat and protein content.

The rheological behaviour of meat batters during heating was analysed as a function of protein level (10-16%), type (pork back or perirenal/peritoneal fat) and amount (10-22%) of fat used. Fat thermal behaviour was studied by differential scanning calorimetry and rheological properties of batters were assessed using non-destructive measurements (thermal scanning rigidity monitor). The higher the protein content, the higher were the rigidity values displayed by the batters, irrespective of fat type, although the magnitude of these values appeared to be dependent on the amount and characteristics of the fat. The lower the fat content, the lower were the rigidity values of the batters. This behaviour pattern was influenced by the amount of protein present. In general, samples containing perirenal/peritoneal fat exhibited lower rigidity values at high temperatures, whereas at less than 35-40 degrees C, the opposite appeared to be the case.

Apparent Digestibility of Dietary Protein as a Function of Protein Level

Apparent Digestibility of Dietary Protein as a Function of Protein Level