Stage-specific proteolysis of mitotic cyclins is fundamental to eukaryotic cell cycle regulation. We found that yeast Hct1, a conserved protein of eukaryotes, is a necessary and rate-limiting component of this proteolysis pathway. In hct1 mutants, the mitotic cyclin Clb2 is highly stabilized and inappropriately induces DNA replication, while G1 cyclins and other proteolytic substrates remain short-lived. Viability of hct1 mutants depends on SIC1. This and further results suggest that inhibition of cyclin-dependent kinases may compensate for defects in cyclin proteolysis. Remarkably, elevated levels of Hct1 ectopically activate destruction box- and Cdc23-dependent degradation of Clb2 and cause phenotypic effects characteristic for a depletion of M-phase cyclins. Hct1 and the related Cdc20 may function as substrate-specific regulators of proteolysis during mitosis.

Proteolysis of mitotic cyclins depends on a multisubunit ubiquitin-protein ligase, the anaphase promoting complex (APC). Proteolysis commences during anaphase, persisting throughout G1 until it is terminated by cyclin-dependent kinases (CDKs) as cells enter S phase. Proteolysis of mitotic cyclins in yeast was shown to require association of the APC with the substrate-specific activator Hct1 (also called Cdh1). Phosphorylation of Hct1 by CDKs blocked the Hct1-APC interaction. The mutual inhibition between APC and CDKs explains how cells suppress mitotic CDK activity during G1 and then establish a period with elevated kinase activity from S phase until anaphase.

The SCF (Skp1-Cullin-F-box) E3 ubiquitin ligase family was discovered through genetic requirements for cell cycle progression in budding yeast. In these multisubunit enzymes, an invariant core complex, composed of the Skp1 linker protein, the Cdc53/Cul1 scaffold protein and the Rbx1/Roc1/Hrt1 RING domain protein, engages one of a suite of substrate adaptors called F-box proteins that in turn recruit substrates for ubiquitination by an associated E2 enzyme. The cullin-RING domain-adaptor architecture has diversified through evolution, such that in total many hundreds of distinct SCF and SCF-like complexes enable degradation of myriad substrates. Substrate recognition by adaptors often depends on posttranslational modification of the substrate, which thus places substrate stability under dynamic regulation by intracellular signaling events. SCF complexes control cell proliferation through degradation of critical regulators such as cyclins, CDK inhibitors and transcription factors. A plethora of other processes in development and disease are controlled by other SCF-like complexes, including those based on Cul2-SOCS-box adaptor protein and Cul3-BTB domain adaptor protein combinations. Recent structural insights into SCF-like complexes have begun to illuminate aspects of substrate recognition and catalytic reaction mechanisms.

ObjectiveThe authors reviewed the hemorrhagic complications of patients who underwent pancreatoduodenectomies between 1972 and 1996. Summary Background DataAlthough recent studies have demonstrated a reduction in the mortality of pancreatic resection, morbidity is still high. Bleeding is a close second to anastomotic dehiscence in the list of dangerous postoperative complications. MethodsThe medical records from a prospective data bank of 559 patients who underwent pancreatic resection at the Surgical Clinic of Mannheim (Heidelberg University) were analyzed in regard to postoperative hemorrhagic complications. Differences were evaluated with the Fisher exact test.

Ubiquitin‐mediated proteolysis has emerged as a key mechanism of regulation in eukaryotic cells. During cell division, a multi‐subunit ubiquitin ligase termed the anaphase promoting complex (APC) targets critical regulatory proteins such as securin and mitotic cyclins, and thereby triggers chromosome separation and exit from mitosis. Previous studies in the yeast Saccharomyces cerevisiae identified the conserved WD40 proteins Cdc20 and Hct1 (Cdh1) as substrate‐specific activators of the APC, but their precise mechanism of action has remained unclear. This study provides evidence that Hct1 functions as a substrate receptor that recognizes target proteins and recruits them to the APC for ubiquitylation and subsequent proteolysis. By co‐immunoprecipitation, we found that Hct1 interacted with the mitotic cyclins Clb2 and Clb3 and the polo‐related kinase Cdc5, whereas Cdc20 interacted with the securin Pds1. Failure to interact with Hct1 resulted in stabilization of Clb2. Analysis of Hct1 derivatives identified the C‐box, a motif required for APC association of Hct1 and conserved among Cdc20‐related proteins. We propose that proteins of the Cdc20 family are substrate recognition subunits of the ubiquitin ligase APC.

In the Journal's recent series of articles on the future of public health, Pearce argues that epidemiology has become overreductive, attending to personal behaviors at the expense of social and historical factors; he proposes instead a "postmodern epidemiol- The paradigm underlying these efforts was the reductive-objective paradigm of science, which aims at "objective" and "universal" truths, as determined by the scientist. It has clearly evolved, from simple models of cause and effect to complex ecological "webs" of causation," but the search for objective, universal truths has not changed, and the processes of research and intervention are still controlled by the scientist. An ecological approach does help solve some problems, overconcentration on personal behaviors, for example. Complex social factors are indeed also determinants of health and disease. But this complexity can also immobilize; there are so many potentially relevant variables! To work more effectively, and to constitute a new paradigm, we need something more. Community participation-the involvement of people in designing and implementing research and interventions intended to benefit them-emerges from public health practice to satisfy this need. We first became aware of its possibilities from the North Karelia Project, Finland's major coronary heart disease intervention in the 1980s. Although similar in scale and methods to the US interventions, it differed from them in two important ways.

Quorum quenching lactonases are enzymes that are capable of disrupting bacterial signaling based on acyl homoserine lactones (AHL) via their enzymatic degradation. In particular, lactonases have therefore been demonstrated to inhibit bacterial behaviors that depend on these chemicals, such as the formation of biofilms or the expression of virulence factors. Here we characterized biochemically and structurally a novel representative from the metallo-β-lactamase superfamily, named AaL that was isolated from the thermoacidophilic bacterium Alicyclobacillus acidoterrestris. AaL is a potent quorum quenching enzyme as demonstrated by its ability to inhibit the biofilm formation of Acinetobacter baumannii. Kinetic studies demonstrate that AaL is both a proficient and a broad spectrum enzyme, being capable of hydrolyzing a wide range of lactones with high rates (kcat/KM > 105 M−1.s−1). Additionally, AaL exhibits unusually low KM values, ranging from 10 to 80 µM. Analysis of AaL structures bound to phosphate, glycerol, and C6-AHL reveals a unique hydrophobic patch (W26, F87 and I237), involved in substrate binding, possibly accounting for the enzyme’s high specificity. Identifying the specificity determinants will aid the development of highly specific quorum quenching enzymes as potential therapeutics.

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