Keeping dissection alive for medical students.

Traditional dissection teaching is being reduced in a number of medical schools, particularly in the United Kingdom. In response to this, 12 medical students from Warwick University, UK, traveled to the Island of Grenada for an intensive extracurricular dissection course at St. George's University. This course not only benefited the host university through the creation of prosections for teaching but also allowed the participants to completely immerse themselves in anatomical study, by developing their dissection skills and consolidating anatomical knowledge. We believe that similar courses could be easily implemented by other medical schools, thereby allowing future students to keep traditional dissection alive.

RbcX can function as a rubisco chaperonin, but is non-essential in Synechococcus PCC7942.

In most cyanobacteria, the gene rbcX is co-transcribed with the rbcL and rbcS genes that code for the large and small subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Previous co-expression studies in Escherichia coli of cyanobacterial Rubisco and RbcX have identified a chaperonin-like function for RbcX. The organization of the rbcLXS operon has, to a certain extent, precluded definitive gene function studies of rbcX in cyanobacteria. In Synechococcus PCC7942, however, rbcX is located >100 kb away from the rbcLS operon, providing an opportunity to examine the role of RbcX by insertional inactivation without interference from the Rubisco genes. Fully segregated Synechococcus PCC7942 DeltarbcX::KmR mutants were readily obtained that showed no perturbations in growth rate or Rubisco content and activity. Low amounts of rbcX transcript were detected in Synechococcus PCC7942; however, a sensitive antibody raised against purified RbcX failed to detect RbcX expression in cells exposed to different stress treatments. In contrast, co-expression studies of Rubisco assembly in E. coli showed that RbcX from Synechococcus PCC7942 and PCC7002 are functionally interchangeable and can stimulate assembly of the PCC7942 and PCC7002 Rubisco subunits. Our results indicate that Rubisco folding and assembly in Synechococcus PCC7942 may have evolved to be independent of RbcX function, apparently in contrast to other beta-cyanobacteria. We speculate that divergent evolution of the RbcL sequence may have relaxed a requirement for RbcX function in Synechococcus PCC7942 and propose a new approach for definitively isolating RbcX function in other beta-cyanobacteria.

State transitions: an example of acclimation to low-light stress.

State 1-State 2 transitions ('state transitions') are a rapid physiological adaptation mechanism that adjusts the way absorbed light energy is distributed between photosystem I and photosystem II. They occur in both green plants and cyanobacteria, although the light-harvesting complexes involved are very different. Which aspects of the mechanism are conserved in green plants and cyanobacteria and which may be different, are discussed. It is shown that phycobilisome mobility is necessary for state transitions in cyanobacteria. A conserved cyanobacterial gene (rpaC) that plays a very specific role in state transitions has been identified. There is still debate about the physiological role of state transitions. Comparison of the growth properties of the rpaC deletion mutant with the wild-type gives us a way of directly addressing the question. It was found that state transitions are physiologically important only at very low light intensities: they play no role in protection from photoinhibition. Thus state transitions are a way to maximize the efficiency of light-harvesting at low light intensities.

Nitrogen-regulated hypermutator strain of Synechococcus sp. for use in in vivo artificial evolution.

Artificially evolved variants of proteins with roles in photosynthesis may be selected most conveniently by using a photosynthetic organism, such as a cyanobacterium, whose growth depends on the function of the target protein. However, the limited transformation efficiency of even the most transformable cyanobacteria wastes much of the diversity of mutant libraries of genes produced in vitro, impairing the coverage of sequence space. This highlights the advantages of an in vivo approach for generating diversity in the selection organism itself. We constructed two different hypermutator strains of Synechococcus sp. strain PCC 7942 by insertionally inactivating or nutritionally repressing the DNA mismatch repair gene, mutS. Inactivation of mutS greatly increases the mutation rate of the cyanobacterium's genes, leading to an up-to-300-fold increase in the frequency of resistance to the antibiotics rifampin and spectinomycin. In order to control the rate of mutation and to limit cellular damage resulting from prolonged hypermutation, we placed the uninterrupted mutS gene in the cyanobacterial chromosome under the transcriptional control of the cyanobacterial nirA promoter, which is repressed in the presence of NH(4)(+) as an N source and derepressed in its absence. By removing or adding this substrate, hypermutation was activated or repressed as required. As expected, hypermutation caused by repression in PnirA-mutS transformants led to an accumulation of spectinomycin resistance mutations during growth.