Properties of an in vitro selected Pb2+ cleavage motif

The addition of Pb 2+ to a small RNA molecule consisting of an asymmetric internal loop of six nucleotides results in site-specific cleavage followed by hydrolysis of the 2′,3′-cyclic phosphate intermediate [Pan, T., & Uhlenbeck, O. C. (1992) Nature 358, 560-563]. Here we show that the reaction is highly specific for Pb 2+ and the cleavage rate increases exponentially with pH from 5.5 to 7.0, both in the presence and in the absence of Mg 2+. This suggests that the reaction mechanism involves Pb 2+ hydroxide acting as a base. Several sequence variants of the RNA are found to be equally active in both steps of the reaction, suggesting that they fold into a similar structure.

Specific recognition of the HIV-1 genomic RNA by the Gag precursor

During assembly of HIV-1 particles in infected cells, the viral Pr55(Gag) protein (or Gag precursor) must select the viral genomic RNA (gRNA) from a variety of cellular and viral spliced RNAs. However, there is no consensus on how Pr55(Gag) achieves this selection. Here, by using RNA binding and footprinting assays, we demonstrate that the primary Pr55(Gag) binding site on the gRNA consists of the internal loop and the lower part of stem-loop 1 (SL1), the upper part of which initiates gRNA dimerization. A double regulation ensures specific binding of Pr55(Gag) to the gRNA despite the fact that SL1 is also present in spliced viral RNAs. The region upstream of SL1, which is present in all HIV-1 RNAs, prevents binding to SL1, but this negative effect is counteracted by sequences downstream of SL4, which are unique to the gRNA.

Closing the loop on student evaluations

It is generally agreed that good teaching is dependent on the nature of the learning goals and the quality of the environment in which learning takes place1,2. If this is the case, then planned as opposed to unplanned variations in learning experiences are the hallmark of good teaching. This raises a complex set of relations between assuring and improving teaching within an institution. The essential question for a University is: how do we assure that learning is maximised in all given contexts?

Benchmarking the use of student feedback was identified as a priority project at the ATN annual conference in February 2002. This paper presents a number of issues arising from a study of practices across the ATN in relation to collecting, analysing and using student feedback. The project involved working with those responsible for teaching and learning improvements at the operational level to identify strategies for a systematic approach to the use of student feedback for improving communication of actions arising from results.

The framework for the inquiry involved an exploration of student feedback systems as they operate for different cohorts of students, differing measures (or constructs), and at different levels within institutional structures. The framework also explored the various tracking and reporting systems by which results generated from student feedback systems at each level were utilised to develop strategies for improving teaching and learning. Findings from the study were used to inform recommendations in relation to internal practices within each University, as well as initiatives for benchmarking student evaluation results across universities within the ATN network.