Arabidopsis inositol phosphate kinases IPK1 and ITPK1 constitute a metabolic pathway in maintaining phosphate homeostasis

Emerging studies have suggested that there is a close link between inositol phosphate (InsP) metabolism and cellular phosphate (P_i) homeostasis in eukaryotes; however, whether a common InsP species is deployed as an evolutionarily conserved metabolic messenger to mediate P_i signaling remains unknown. Here, using genetics and InsP profiling combined with P_i‐starvation response (PSR) analysis in Arabidopsis thaliana, we showed that the kinase activity of inositol pentakisphosphate 2‐kinase (IPK1), an enzyme required for phytate (inositol hexakisphosphate; InsP₆) synthesis, is indispensable for maintaining P_i homeostasis under P_i‐replete conditions, and inositol 1,3,4‐trisphosphate 5/6‐kinase 1 (ITPK1) plays an equivalent role. Although both ipk1‐1 and itpk1 mutants exhibited decreased levels of InsP₆ and diphosphoinositol pentakisphosphate (PP‐InsP₅; InsP₇), disruption of another ITPK family enzyme, ITPK4, which correspondingly caused depletion of InsP₆ and InsP₇, did not display similar P_i‐related phenotypes, which precludes these InsP species from being effectors. Notably, the level of d /l ‐Ins(3,4,5,6)P₄ was concurrently elevated in both ipk1‐1 and itpk1 mutants, which showed a specific correlation with the misregulated P_i phenotypes. However, the level of d /l ‐Ins(3,4,5,6)P₄ is not responsive to P_i starvation that instead manifests a shoot‐specific increase in the InsP₇ level. This study demonstrates a more nuanced picture of the intersection of InsP metabolism and P_i homeostasis and PSRs than has previously been elaborated, and additionally establishes intermediate steps to phytate biosynthesis in plant vegetative tissues.     

单链胰岛素前体在酵母中的分泌表达及其转变成人胰岛素

将化学合成的单链猪胰岛素前体(PIP)基因和用聚合酶链反应得到的α交配因子前导顺序(αMFL)基因插入质粒pVT102-U的醇脱氢酶基因ADH1的启动子和3’终止顺序之间而生成质粒pVT102-U/αMFL-PIP.被pVT102-U/αMFL-PIP转化的酵母(Saccharomyces cerevistae)可表达单链前体并分泌到培养基中.前体在纯化后可通过胰蛋白酶的转肽作用转变成人胰岛素.纯化的人胰岛素具有全部活力并可结晶.人胰岛素的总收率为每升培养液25mg.     

Molecular phylogeny of the springhare, Pedetes capensis, based on mitochondrial DNA sequences

The phylogenetic position of the Pedetidae, represented by a single species Pedetes capensis, is controversial, reflecting in part the retention of both Hystricomorphous and Sciurognathous characteristics in this rodent. In an attempt to clarify the species evolutionary relationships, mtDNA gene sequences from 10 rodent species (representing seven families) were analyzed using phenetic, parsimony, and maximum-likelihood methods of phylogenetic inference; the rabbit, Oryctolagus cuniculus (Order Lagomorpha), and cow, Bos taurus (Order Artiodactyla), were used as outgroups. Investigation of 714 base pairs of the protein-coding cytochrome b gene indicate strong base bias at the third codon position with significant rate heterogeneity evident between the three structural domains of this gene. Similar analyses conducted on 816 base pairs of the 12S rRNA gene revealed a transversion bias in the loop sections of all taxa. The cytochrome b gene sequences proved useful in resolving associations between closely related species but failed to produce consistent tree topologies at the family level. In contrast, phylogenetic analysis of the 12S rRNA gene resulted in strong support for the clustering of Pedetidae/Heteromyidae/Geomyidae and Muridae in one clade to the exclusion of the Hystricidae/Thryonomyidae and Sciuridae, a finding which is concordant with studies of rodent fetal membranes as well as reproductive and other anatomical features.      

Prognostic significance of cell surface phenotype in adult acute lymphoblastic leukaemia

Summary Forty-two adults with acute lymphoblastic leukaemia were subgrouped according to the membrane marker characteristics of their blast cells. All patients received the same treatment at St. Bartholomew's Hospital. The results indicate that the group expressing the common ALL antigen have a superior remission duration to the ALL antigen-negative, non-T, non-B ALL group and the T-ALL group. No correlation was evident between the first two subgroups and the clinical features of disease.     

The Arabidopsis ATP-binding Cassette Protein AtMRP5/AtABCC5 Is a High Affinity Inositol Hexakisphosphate Transporter Involved in Guard Cell Signaling and Phytate Storage

Arabidopsis possesses a superfamily of ATP-binding cassette (ABC) transporters. Among these, the multidrug resistance-associated protein AtMRP5/AtABCC5 regulates stomatal aperture and controls plasma membrane anion channels of guard cells. Remarkably, despite the prominent role of AtMRP5 in conferring partial drought insensitivity upon Arabidopsis, we know little of the biochemical function of AtMRP5. Our phylogenetic analysis showed that AtMRP5 is closely related to maize MRP4, mutation of which confers a low inositol hexakisphosphate kernel phenotype. We now show that insertion mutants of AtMRP5 display a low inositol hexakisphosphate phenotype in seed tissue and that this phenotype is associated with alterations of mineral cation and phosphate status. By heterologous expression in yeast, we demonstrate that AtMRP5 encodes a specific and high affinity ATP-dependent inositol hexakisphosphate transporter that is sensitive to inhibitors of ABC transporters. Moreover, complementation of the mrp5-1 insertion mutants of Arabidopsis with the AtMRP5 cDNA driven from a guard cell-specific promoter restores the sensitivity of the mutant to abscisic acid-mediated inhibition of stomatal opening. Additionally, we show that mutation of residues of the Walker B motif prevents restoring the multiple phenotypes associated with mrp5-1. Our findings highlight a novel function of plant ABC transporters that may be relevant to other kingdoms. They also extend the signaling repertoire of this ubiquitous inositol polyphosphate signaling molecule.