Genetic and biochemical evidence for distinct key functions of two highly divergent GAPDH genes in catabolic and anabolic carbon flow of the cyanobacterium Synechocystis sp. PCC 6803

Cyanobacterial genomes harbour two separate highly divergent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes, gap1 and gap2, which are closely related at the sequence level to the nuclear genes encoding cytosolic and chloroplast GAPDH of higher plants, respectively. Genes gap1 and gap2 of the unicellular cyanobacterium Synechocystis sp. PCC 6803 were cloned and sequenced and subsequently inactivated by insertional mutagenesis to understand their metabolic functions. We obtained homozygous gap1^- mutants which have lost the capacity to grow on glucose under dim light while growth on organic acids as well as photosynthetic growth under CO₂ and high light is not impaired. Homozygous gap2^- mutants show the reciprocal phenotype. Under dim light they only grow on glucose but not on organic acids nor do they survive under photosynthetic conditions. Measurements of the anabolic activities (reduction of 1,3-bisphosphoglycerate) in extracts from wild type and mutant cells show that Gap2 is a major enzyme with dual cosubstrate specificity for NAD and NADP, while Gap1 displays a minor NAD-specific GAPDH activity. However, if measured in the catabolic direction (oxidation of glyceraldehyde-3-phosphate) Gap2 activity is very low and increases three- to fivefold after gel filtration of extracts over Sephadex G25. Our results suggest that enzymes Gap1 and Gap2, although coexpressed in cyanobacterial wild-type cells, play distinct key roles in catabolic and anabolic carbon flow, respectively. While Gap2 operates in the photosynthetic Calvin cycle and in non-photosynthetic gluconeogenesis, Gap1 seems to be essential only for glycolytic glucose breakdown, conditions under which the catabolic activity of Gap2 seems to be repressed by a specific low-molecular-weight inhibitor.     

核骨架——细胞核内生命活动的重要结构体系

综合分析了国际国内近年来有关核骨架研究的新进展,从几个方面的研究事实,包括核骨架对染色质ＤＮＡ的有序组织,核骨架参与ＤＮＡ复制和基因的表达与调控以及核骨架的起源进化等,阐明核骨架是细胞核内染色质结构的有序组织者和功能活动的参与者,核内纷繁复杂的生命活动能有条不紊地进行,核骨架在其中扮演了重要角色。     

Limits to water transport in Juniperus osteosperma and Pinus edulis: implications for drought tolerance and regulation of transpiration

1. An air-injection method was used to study loss of water transport capacity caused by xylem cavitation in roots and branches of Pinus edulis (Colorado Pinyon) and Juniperus osteosperma (Utah Juniper). These two species characterize the Pinyon–Juniper communities of the high deserts of the western United States. Juniperus osteosperma can grow in drier sites than P. edulis and is considered the more drought tolerant.
2. Juniperus osteosperma was more resistant to xylem cavitation than P. edulis in both branches and roots. Within a species, branches were more resistant to cavitation than roots for P. edulis but no difference was seen between the two organs for J. osteosperma . There was also no difference between juveniles and adults in J. osteosperma ; this comparison was not made for P. edulis .
3. Tracheid diameter was positively correlated with xylem cavitation pressure across roots and stems of both species. This relation suggests a trade-off between xylem conductance and resistance to xylem cavitation in these species.
4. During summer drought, P. edulis maintained higher predawn xylem pressures and showed much greater stomatal restriction of transpiration, consistent with its greater vulnerability to cavitation, than J. osteosperma .
5. These results suggest that the relative drought tolerance of P. edulis and J. osteosperma results in part from difference in their vulnerability to xylem cavitation.     

Use of induction promoters to regulate hyaluronan synthase and UDP-glucose-6-dehydrogenase of Streptococcus zooepidemicus expression in Lactococcus lactis: a case study of the regulation mechanism of hyaluronic acid polymer

Aims:  To determine the effects of the ratios of hyaluronan synthase expression level to precursor sugar UDP-GlcA biosynthesis ability on the molecular weight (MW) of hyaluronic acid (HA) in recombinant Lactococcus lactis .
Methods and Results:  The genes sz HasA (hyaluronan synthase gene) and sz HasB (UDP-glucose-6-dehydrogenase gene) of Streptococcus zooepidemicus were introduced into L. lactis under the control of nisA promoter and lacA promoter respectively, resulting in a dual-plasmid controlled expression system. The effects of the ratios of hyaluronan synthase expression level to the precursor sugar UDP-GlcA biosynthesis ability under different induction concentration collocations with nisin and lactose on the MW of HA in recombinant L. lactis were determined. The results showed that the final weight-average molecular weight (     ) of HA correlated with the relative ratios of HasA (hyaluronan synthase) expression level to the concentration of UDP-GlcA.
Conclusions:  Regulating the relative ratios of HasA expression level to the precursor sugar biosynthesis ability was an efficient method to control the size of HA.
Significance and Impact of the Study:  This study put forward a guide to establish an efficacious way to control the size of HA in fermentation.     

DNA bridging and antibridging: a role for bacterial nucleoid-associated proteins in regulating the expression of laterally acquired genes

Horizontal DNA transfer plays a major role in the evolution of bacteria. It allows them to acquire new traits rapidly and these may confer fitness advantages as the bacteria compete with others in the environment. Historically, the mechanisms of horizontal DNA transfer, chiefly conjugation, transformation and transduction, have received a great deal of attention. Less attention has been focused on the regulatory problems that may accompany the acquisition of new genes by lateral routes. How are these genes integrated into the existing regulatory circuits of the cell? Does a process of 'plug-and-play' operate, or are the new genes silenced pending the evolution of regulatory mechanisms that make their expression not only safe but also beneficial to both the gene and its new host? Recent research shows that bacterial nucleoid-associated proteins such as H-NS, HU and Fis are important contributors to the processes of regulatory integration that accompany horizontal gene transfer. A key emerging theme is the antagonism that exists between the DNA–protein–DNA bridging activity of the H-NS repressor and the DNA-bending and DNA-wrapping activities of regulatory proteins that oppose H-NS.     

The Level of Expression of Thioredoxin is Linked to Fundamental Properties and Applications of Wheat Seeds

Work with cereals （barley and wheat） and a legume （Medicago truncatula） has established thioredoxin h （Trx h） as a central regulatory protein of seeds. Trx h acts by reducing disulfide （S-S） groups of diverse seed proteins （storage proteins, enzymes, and enzyme inhibitors）, thereby facilitating germination. Early in vitro protein studies were complemented with experiments in which barley seeds with Trx h overexpressed in the endosperm showed accelerated germination and early or enhanced expression of associated enzymes （α-amylase and pullulanase）. The current study extends the transgenic work to wheat. Two approaches were followed to alter the expression of Trx h genes in the endosperm： （1） a hordein promoter and its protein body targeting sequence led to overexpression of Trx hS, and （2） an antisense construct of Trx h9 resulted in cytosolic underexpression of that gene （Arabidopsis designation）. Underexpression of Trx h9 led to effects opposite to those observed for overexpression Trx h5 in barley--retardation of germination and delayed or reduced expression of associated enzymes. Similar enzyme changes were observed in developing seeds. The wheat lines with underexpressed Trx showed delayed preharvest sprouting when grown in the greenhouse or field without a decrease in final yield. Wheat with overexpressed Trx h5 showed changes commensurate with earlier in vitro work： increased solubility of disulfide proteins and lower aUergenicity of the gliadin fraction. The results are further evidence that the level of Trx h in cereal endosperm determines fundamental properties as well as potential applications of the seed.