Audience response systems (ARS) or clickers, as they are commonly called, offer a management tool for engaging students in the large classroom. Basic elements of the technology are discussed. These systems have been used in a variety of fields and at all levels of education. Typical goals of ARS questions are discussed, as well as methods of compensating for the reduction in lecture time that typically results from their use. Examples of ARS use occur throughout the literature and often detail positive attitudes from both students and instructors, although exceptions do exist. When used in classes, ARS clickers typically have either a benign or positive effect on student performance on exams, depending on the method and extent of their use, and create a more positive and active atmosphere in the large classroom. These systems are especially valuable as a means of introducing and monitoring peer learning methods in the large lecture classroom. So that the reader may use clickers effectively in his or her own classroom, a set of guidelines for writing good questions and a list of best-practice tips have been culled from the literature and experienced users.

We have studied the interaction of CapZ, a barbed-end actin capping protein from the Z line of skeletal muscle, with actin. CapZ blocks actin polymerization and depolymerization (i.e., it "caps") at the barbed end with a Kd of approximately 0.5-1 nM or less, measured by three different assays. CapZ inhibits the polymerization of ATP-actin onto filament ends with ATP subunits slightly less than onto ends with ADP subunits, and onto ends with ADP-BeF3- subunits about as much as ends with ADP subunits. No effect of CapZ is seen at the pointed end by measurements either of polymerization from acrosomal processes or of the critical concentration for polymerization at steady state. CapZ has no measureable ability to sever actin filaments in a filament dilution assay. CapZ nucleates actin polymerization at a rate proportional to the first power of the CapZ concentration and the 2.5 power of the actin concentration. No significant binding is observed between CapZ and rhodamine-labeled actin monomers by fluorescence photobleaching recovery. These new experiments are consistent with but do not distinguish between three models for nucleation proposed previously (Cooper & Pollard, 1985). As a prelude to the functional studies, the purification protocol for CapZ was refined to yield 2 mg/kg of chicken breast muscle in 1 week. The activity is stable in solution and can be lyophilized. The native molecular weight is 59,600 +/- 2000 by equilibrium ultracentrifugation, and the extinction coefficient is 1.25 mL mg-1 cm-1 by interference optics. Polymorphism of the alpha and beta subunits has been detected by isoelectric focusing and reverse-phase chromatography. CapZ contains no phosphate (less than 0.1 mol/mol).

The fruit of Pentadiplandra brazzeana Baillon contains a small, sweet-tasting protein named brazzein. The structure of brazzein in solution was determined by proton nuclear magnetic resonance spectroscopy at pH 5.2 and 22 degrees C. The brazzein fold, which contains one alpha-helix and three strands of antiparallel beta-sheet, does not resemble that of either of the other two sweet-tasting proteins with known structures, monellin and thaumatin. Instead, the structure of brazzein resembles those of plant gamma-thionins and defensins and arthropod toxins. Sequence comparisons predict that members of a newly-identified family of serine proteinase inhibitors share the brazzein fold.

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Chicken adult muscle and liver cDNA libraries were screened with a cDNA, alpha 1, previously isolated from a chicken embryo library by screening with antibodies against the alpha subunit of chicken CapZ. cDNAs with a new coding region, called alpha 2, were found in addition to ones with the alpha 1 coding region. alpha 2 predicts a protein sequence that matches exactly the N-terminal sequence of 5 peptides prepared from CapZ alpha purified from chicken muscle, while the protein sequence predicted by alpha 1 matches the peptides well, but not exactly. The predicted protein sequences of alpha 1 and alpha 2 are very similar to each other, and they are similar to those of the alpha subunit of capping protein from Dictyostelium [Hartmann et al., J. Biol. Chem. 163:5254-5254, 1989] and an actin-binding protein from Xenopus [Ankenbauer et al., Nature 342:822-824, 1989]. Other conserved features of the predicted primary and secondary structures are noted. Chicken alpha 1 and alpha 2 are transcribed in all of 7 adult chicken muscle and non-muscle tissues in comparable amounts by Northern analysis. alpha 2 has four poly(A)+RNA transcripts, one of which is rare in liver. alpha 1 has two transcripts. alpha 1 and alpha 2 are encoded by different single-copy genes by Southern analysis of chicken genomic DNA.

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