ABSTRACT
AIM: This in vitro study was carried out to compare the effect of LED light curing system on polymerization and hardness of silorane-based and methacrylate-based posterior composite resin. MATERIALS AND METHODS: A total of 40 samples, 20 of silorane-based composite Filtek P-90 and 20 of methacrylate-based composite Heliomolar HB measuring 2 mm thickness and 8 mm diameter were prepared using Teflon molds and cured using LED curing light. The samples were polished and tested in Knoop hardness tester using a 50-gram load and dwell time of 15 seconds on top and bottom surfaces. The percentage depth of cure was calculated, and statistical analysis was performed using two-way ANOVA test and Student t- test. RESULTS: Higher statistically significant values were seen for both the top and bottom surface hardness in silorane-based resins than methacrylate-based resins on LED light curing. CONCLUSION: Greater depth of cure was achieved in silorane-based posterior composite than in methacrylate-based posterior composite resins with a statistically significant difference.
ABSTRACT
The crystal structure of a Flp recombinase tetramer bound to a Holliday junction intermediate has been determined at 2.65 A resolution. Only one of Flp's two domains, containing the active site, is structurally related to other lambda integrase family site-specific recombinases, such as Cre. The Flp active site differs, however, in that the helix containing the nucleophilic tyrosine is domain swapped, such that it cuts its DNA target in trans. The Flp tetramer displays pseudo four-fold symmetry matching that of the square planar Holliday junction substrate. This tetramer is stabilized by additional novel trans interactions among monomers. The structure illustrates how mechanistic unity is maintained on a chemical level while allowing for substantial variation on the structural level within a family of enzymes.
Subject(s)
DNA Nucleotidyltransferases/chemistry , DNA Nucleotidyltransferases/metabolism , DNA/chemistry , DNA/metabolism , Recombination, Genetic , Amino Acid Sequence , Base Sequence , Binding Sites , Crystallography, X-Ray , Models, Genetic , Models, Molecular , Molecular Sequence Data , Nucleic Acid Conformation , Oligodeoxyribonucleotides/chemistry , Protein Conformation , Protein Structure, SecondaryABSTRACT
Sex determination is regulated by diverse pathways. Although upstream signals vary, a cysteine-rich DNA-binding domain (the DM motif) is conserved within downstream transcription factors of Drosophila melanogaster (Doublesex) and Caenorhabditis elegans (MAB-3). Vertebrate DM genes have likewise been identified and, remarkably, are associated with human sex reversal (46, XY gonadal dysgenesis). Here we demonstrate that the structure of the Doublesex domain contains a novel zinc module and disordered tail. The module consists of intertwined CCHC and HCCC Zn(2+)-binding sites; the tail functions as a nascent recognition alpha-helix. Mutations in either Zn(2+)-binding site or tail can lead to an intersex phenotype. The motif binds in the DNA minor groove without sharp DNA bending. These molecular features, unusual among zinc fingers and zinc modules, underlie the organization of a Drosophila enhancer that integrates sex- and tissue-specific signals. The structure provides a foundation for analysis of DM mutations affecting sexual dimorphism and courtship behavior.
