IntAct is an open source database and software suite for modeling, storing and analyzing molecular interaction data. The data available in the database originates entirely from published literature and is manually annotated by expert biologists to a high level of detail, including experimental methods, conditions and interacting domains. The database features over 126 000 binary interactions extracted from over 2100 scientific publications and makes extensive use of controlled vocabularies. The web site provides tools allowing users to search, visualize and download data from the repository. IntAct supports and encourages local installations as well as direct data submission and curation collaborations. IntAct source code and data are freely available from .

To gain insight into the synthesis and functions of enzymes of starch metabolism in leaves of Arabidopsis L. Heynth, Affymetrix microarrays were used to analyze the transcriptome throughout the diurnal cycle. Under the conditions employed, transitory leaf starch is degraded progressively during a 12-h dark period, and then accumulates during the following 12-h light period. Transcripts encoding enzymes of starch synthesis changed relatively little in amount over 24 h except for two starch synthases, granule bound starch synthase and starch synthase II, which increased appreciably during the transition from dark to light. The increase in RNA encoding granule-bound starch synthase may reflect the extensive destruction of starch granules in the dark. Transcripts encoding several enzymes putatively involved in starch breakdown showed a coordinated decline in the dark followed by rapid accumulation in the light. Despite marked changes in their transcript levels, the amounts of some enzymes of starch metabolism do not change appreciably through the diurnal cycle. Posttranscriptional regulation is essential in the maintenance of amounts of enzymes and the control of their activities in vivo. Even though the relationships between transcript levels, enzyme activity, and diurnal metabolism of starch metabolism are complex, the presence of some distinctive diurnal patterns of transcripts for enzymes known to be involved in starch metabolism facilitates the identification of other proteins that may participate in this process.Starch is the major form in which carbon is stored in plants, the major source of calories in the human diet, and an important industrial commodity (Jobling, 2004). However, our understanding of the nature and regulation of the pathways of starch synthesis and degradation is incomplete. The Arabidopsis genome sequence, together with extensive functional genomics resources, is facilitating investigations to better understand starch metabolism in plants (Zeeman et al., 2002;Smith et al., 2003). Starch is synthesized in many organs of Arabidopsis, including leaves, flowers, developing seeds, and root caps, and the structure and composition of starch isolated from leaves are similar to that from crop plants (Zeeman et al., 2002). Use of leaves enables both synthesis and degradation to be studied within a 24-h period independently of changes in plant development. The two processes are integrated with each other, and their rates are related to the duration of day and night. Characteristic changes in the content of sugars and maltooligosaccharides are also observed throughout the diurnal cycle, showing a complex integration of starch and sugar metabolism. The Arabidopsis leaf thus provides an excellent model system with which to elucidate the pathways and regulatory mechanisms of starch synthesis and breakdown in the plastids of living cells (Zeeman et al., 2002;Smith et al., 2003).The Arabidopsis genome sequence reveals many genes encoding enzymes that may be involved in starch synthesis and degradation, and...

SummaryMaltose is exported from the Arabidopsis chloroplast as the main product of starch degradation at night. To investigate its fate in the cytosol, we characterised plants with mutations in a gene encoding a putative glucanotransferase (disproportionating enzyme; DPE2), a protein similar to the maltase Q (MalQ) gene product involved in maltose metabolism in bacteria. Use of a DPE2 antiserum revealed that the DPE2 protein is cytosolic. Four independent mutant lines lacked this protein and displayed a decreased capacity for both starch synthesis and starch degradation in leaves. They contained exceptionally high levels of maltose, and elevated levels of glucose, fructose and other malto-oligosaccharides. Sucrose levels were lower than those in wild-type plants, especially at the start of the dark period. A glucosyltransferase activity, capable of transferring one of the glucosyl units of maltose to glycogen or amylopectin and releasing the other, was identi®ed in leaves of wild-type plants. Its activity was suf®cient to account for the rate of starch degradation. This activity was absent from dpe2 mutant plants. Based on these results, we suggest that DPE2 is an essential component of the pathway from starch to sucrose and cellular metabolism in leaves at night. Its role is probably to metabolise maltose exported from the chloroplast. We propose a pathway for the conversion of starch to sucrose in an Arabidopsis leaf.