Long-term changes in the structure of benthic communities: Revisiting a sampling transect in Crete after 24 years.

A bathymetric transect in the north coast of Crete first studied in 1989, was revisited 24 years later. Identical sampling design, season, techniques and protocols were followed in both studies in order to minimize bias in the long-term comparisons. This comprehensive macrofaunal dataset (4 stations, 2 sampling seasons, 7 replicates in each study) revealed changes in benthic diversity and community composition between the sampling periods. The recorded changes were higher at the stations located close to the coastal zone. In addition, while benthic communities showed lower total abundance during the recent sampling period, species abundances were more evenly distributed indicating that some species dominated the historical communities. In spite of these changes, the ecological status remained above the threshold values for good ecological status. The results indicated that changes in the benthic community seem to have been driven by local anthropogenic factors and natural variability rather than by large-scale factors such as nutrients influxes in the entire Mediterranean Basin.

Ion concentration and temperature dependence of DNA binding: comparison of PurR and LacI repressor proteins.

Purine repressor (PurR) binding to specific DNA is enhanced by complexing with purines, whereas lactose repressor (LacI) binding is diminished by interaction with inducer sugars despite 30% identity in their protein sequences and highly homologous tertiary structures. Nonetheless, in switching from low- to high-affinity DNA binding, these proteins undergo a similar structural change in which the hinge region connecting the DNA and effector binding domains folds into an alpha-helix and contacts the DNA minor groove. The differences in response to effector for these proteins should be manifest in the polyelectrolyte effect which arises from cations displaced from DNA by interaction with positively charged side chains on a protein and is quantitated by measurement of DNA binding affinity as a function of ion concentration. Consistent with structural data for these proteins, high-affinity operator DNA binding by the PurR-purine complex involved approximately 15 ion pairs, a value significantly greater than that for the corresponding state of LacI (approximately 6 ion pairs). For both proteins, however, conversion to the low-affinity state results in a decrease of approximately 2-fold in the number of cations released per dimeric DNA binding site. Heat capacity changes (DeltaC(p)) that accompany DNA binding, derived from buried apolar surface area, coupled folding, and restriction of motional freedom of polar groups in the interface, also reflect the differences between these homologous repressor proteins. DNA binding of the PurR-guanine complex is accompanied by a DeltaC(p) (-2.8 kcal mol(-1) K(-1)) more negative than that observed previously for LacI (-0.9 to -1.5 kcal mol(-1) K(-1)), suggesting that more extensive protein folding and/or enhanced structural rigidity may occur upon DNA binding for PurR compared to DNA binding for LacI. The differences between these proteins illustrate plasticity of function despite high-level sequence and structural homology and undermine efforts to predict protein behavior on the basis of such similarities.

Chronic bronchitis in rural and industrial areas.

The purpose of the study was the determination of prevalence of chronic bronchitis in people older than 55 years in rural and industrial areas. 569 people over 55 years old living in central Greece were studied. A protocol was completed for each patient that included smoking habits, job, age, weight, drugs used for respiratory system and symptoms. A chest radiograph was taken for each patient. Each patient was submitted to three trials of dynamic spirometry. The best results were used for the study. The patients who complained of expectoration for three months for two continuous years and had obstructive pattern of lung function were diagnosed with chronic bronchitis. 9.6% of the subjects in rural area and 17.1% in industrial area were diagnosed with chronic bronchitis. Half the COPD patients never visited a doctor for this specific problem and were diagnosed for the first time. One out of three examined people had abnormal lung function. Consequently, more than one out of ten people older than 55 years have chronic bronchitis. Industrial exposure seems to double the risk for chronic bronchitis.

Kinetic and thermodynamic studies of purine repressor binding to corepressor and operator DNA.

The kinetic and thermodynamic parameters for purine repressor (PurR)-operator and PurR-guanine binding were determined using fluorescence spectroscopy and nitrocellulose filter binding. Operator binding affinity was increased by the presence of guanine as demonstrated previously (Choi, K. Y., Lu, F., and Zalkin, H. (1994) J. Biol. Chem. 269, 24066-24072; Rolfes, R. J., and Zalkin, H. (1990) J. Bacteriol. 172, 5637-5642), and conversely guanine binding affinity was increased by the presence of operator. Guanine enhanced operator affinity by increasing the association rate constant and decreasing the dissociation rate constant for binding. Operator had minimal effect on the association rate constant for guanine binding; however, this DNA decreased the dissociation rate constant for corepressor by approximately 10-fold. Despite significant sequence and structural similarity between PurR and LacI proteins, PurR binds to its corepressor ligand with a lower association rate constant than LacI binds to its inducer ligand. However, the rate constant for PurR-guanine binding to operator is approximately 3-fold higher than for LacI binding to its cognate operator under the same solution conditions. The distinct metabolic roles of the enzymes under regulation by these two repressor proteins provide a rationale for the observed functional differences.