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<jats:title>Single-molecule assay of ubiquitylation</jats:title> <jats:p> Many biological processes in cells are regulated by ubiquitin peptides that are attached to proteins. Measurement of single fluorescent molecules in cell extracts can be used to trace the kinetics of such reactions. Lu <jats:italic>et al.</jats:italic> refined assay conditions to follow ubiquitination by an E3 ubiquitin ligase (see the Perspective by Komander). They visualized the activity of the anaphase-promoting complex (APC), a ubiquitin ligase critical for control of the cell division cycle. The processive initial reaction catalyzed by the APC was replaced by slower reactions. The results show how small, commonly occurring recognition motifs can guide specific and highly controlled enzymatic events. In a companion paper, Lu <jats:italic>et al.</jats:italic> explored how the number and arrangement of added ubiquitin chains affected the interaction of ubiquitylated proteins with the proteasome (a protein complex that recognizes ubiquitylated proteins and degrades them). The extent of ubiquitylation determined the strength of interaction of a substrate protein with the proteasome, and the arrangement of the ubiquitin chains determined the movement of the protein into the proteasome and thus the rate of degradation. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.1248737">10.1126/science.1248737</jats:related-article> , <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.1250834">10.1126/science.1250834</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6231" page="183" related-article-type="in-this-issue" vol="348" xlink:href="10.1126/science.aab0931">183</jats:related-article> </jats:p>

<jats:title>Single-molecule assay of ubiquitylation</jats:title> <jats:p> Many biological processes in cells are regulated by ubiquitin peptides that are attached to proteins. Measurement of single fluorescent molecules in cell extracts can be used to trace the kinetics of such reactions. Lu <jats:italic>et al.</jats:italic> refined assay conditions to follow ubiquitination by an E3 ubiquitin ligase (see the Perspective by Komander). They visualized the activity of the anaphase-promoting complex (APC), a ubiquitin ligase critical for control of the cell division cycle. The processive initial reaction catalyzed by the APC was replaced by slower reactions. The results show how small, commonly occurring recognition motifs can guide specific and highly controlled enzymatic events. In a companion paper, Lu <jats:italic>et al.</jats:italic> explored how the number and arrangement of added ubiquitin chains affected the interaction of ubiquitylated proteins with the proteasome (a protein complex that recognizes ubiquitylated proteins and degrades them). The extent of ubiquitylation determined the strength of interaction of a substrate protein with the proteasome, and the arrangement of the ubiquitin chains determined the movement of the protein into the proteasome and thus the rate of degradation. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.1248737">10.1126/science.1248737</jats:related-article> , <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.1250834">10.1126/science.1250834</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6231" page="183" related-article-type="in-this-issue" vol="348" xlink:href="10.1126/science.aab0931">183</jats:related-article> </jats:p>

<jats:p>The U.S. National Institutes of Health (NIH) has for more than 60 years supported research to improve the health and prolong the lives of people in the United States and around the world. Mean life expectancy worldwide has doubled to more than 70 years, due in large part to medical and public health interventions developed with NIH funding. Now, in the face of serious fiscal constraints, the idea has reemerged from some congressional leaders and disease constituency groups to more closely align NIH funding for disease research with disease burden in the United States. Although the nation must maintain robust research support for diseases that cause illness and death among large numbers of Americans, it would be unwise to deemphasize diseases that exact their largest toll elsewhere in the world. The United States has a vital interest in the health of people around the globe, rooted in an enduring tradition of humanitarian concern as well as in enlightened self-interest. Engagement in global health protects the nation's citizens, enhances the economy, and advances U.S. interests abroad.</jats:p>

<jats:p>A roundup of weekly science policy and related news.</jats:p>

<jats:p>Secretive Fordow facility could become a stable isotope factory and international accelerator center.</jats:p>

<jats:p>Signature of acidification found in Permian extinctions 250 million years ago.</jats:p>