A Drosophila homolog of bovine smg p25a GDP dissociation inhibitor undergoes a shift in isoelectric point in the developmental mutant quartet

The Drosophila developmental mutation quartet causes late larval lethality and small imaginal discs and, when expressed in the adult female, has a lethal effect on early embryogenesis. These developmental defects are associated with mitotic defects, which include a low mitotic index in larval brains and incomplete separation of chromosomes in mitosis in the early embryo. quartet mutations also have a biochemical effect, i.e., a basic shift in isoelectric point in three proteins. We have purified one of these proteins, raised an antibody to it, and isolated and sequenced its cDNA. At the amino acid level, the sequence shows 68% identity and 81% similarity to bovine smg p25a GDP dissociation inhibitor (GDI), a regulator of ras-like small GTPases of the rab/SEC4/YPT1 subfamily. The correlation between a basic shift in isoelectric point in Drosophila GDI in quartet mutant tissue and the quartet developmental phenotype raises the possibility that a posttranslational modification of GDI is necessary for its function and that GDI function is essential for development.     

Evolution of the serum amyloid A (SAA) protein superfamily

The serum amyloid A (SAA) superfamily comprises a number of genes and proteins characterized from a range of mammalian species. The majority of members described to date are dramatically induced during the acute-phase response, suggesting an important short-term beneficial role in the response to tissue injury and inflammation. However, important disease associations have also been proposed for certain SAAs during chronic inflammation. The nomenclature of many of the superfamily members has been the result of comparisons with previously reported sequences implying disease association and/or functional relatedness between such members. The evolutionary relationships of the SAA superfamily members have been investigated by comparisons at both the amino acid and the nucleotide level. The results indicate that all members of the superfamily within a species have been undergoing concerted evolution. This has important implications in ascribing functions and disease associations to individual SAA superfamily members and indicates that designations should not be based on the extent of amino acid identity alone but should be made only following direct experimental observation of the proteins themselves.     

Laboratory evaluation of the XR-Bond Dentin/Enamel Bonding System

The shear bond strengths of the XR-Bonding System used in conjunction with Herculite composite, to the dentine of forty extracted human permanent first and second molars were determined after the test specimens were stored in physiological saline at 37 degrees C for 48 hours, one week, two weeks and four weeks, respectively. A shear load was applied to the base of the bonded composite cylinders with a knife-edged rod at a crosshead speed of 0.5 mm/minute. The shear bond strengths were expressed in megapascals (MPa). The quantitative microleakage of Class V preparations in dentine (cementum) in forty-eight extracted human maxillary permanent canines restored with the same dentinal bonding system and after storage in physiological saline at 37 degrees C for the same time intervals as for the shear bond strength tests, was determined. On the final day of each time interval the teeth were thermocycled X 500 in a 2 per cent methylene blue solution between 8 degrees C and 50 degrees C with a dwell time of 15 seconds. Microleakage was determined by a spectrophotometric dye-recovery method and expressed in microgram dye/restoration. There was a significant trend for the shear bond strengths to increase with duration of storage (p = 0.01) but the quantitative microleakage was not significantly different (p = 0.75).