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The yeast Candida glabrata rapidly autoactivates transcription of the AMT1 gene in response to potentially toxic copper levels through the copper-inducible binding of the Amt1 transcription factor to a metal response element (MRE) within a positioned nucleosome. Our previous studies have characterized the role of a 16 bp homopolymeric dA:dT DNA structural element in facilitating rapid Amt1 access to the AMT1 promoter nucleosomal MRE. In this study, we have used the genetically more facile yeast Saccharomyces cerevisiae to identify additional cellular factors that are important for promoting rapid autoactivation of the AMT1 gene in response to toxic copper levels. We demonstrate that the Swi/Snf nucleosome remodelling complex and the histone acetyltransferase Gcn5 are both essential for AMT1 gene autoregulation, and that the requirement for these chromatin remodelling factors is target gene specific. Chromatin accessibility measurements performed in vitro and in vivo indicate that part of the absolute requirement for these factors is derived from their involvement in facilitating nucleosomal access to the AMT1 promoter MRE. Additionally, these data implicate the involvement of Swi/Snf and Gcn5 at multiple levels of AMT1 gene autoregulation.

In vitro temperatures produced in the root canal and on the root surface were measured simultaneously as heated gutta-percha was injected into the prepared canal. The canals were obturated with the Obtura II heated gutta-percha system with temperature settings of 160, 185, and 200 degrees C. The mean intracanal temperatures ranged from 40.21 to 57.24 degrees C, whereas the mean root surface temperatures were recorded from 37.22 to 41.90 degrees C for all three temperatures tested. The rise in temperature on the root surface was below the critical level of 10 degrees C and should not cause damage to the periodontal ligament.

In vitro intracanal temperatures produced by the injection of high-temperature thermoplasticized gutta-percha were measured. Obturations of a standard root canal were performed using an Obtura II heated gutta-percha system at temperature settings of 160, 185, and 200 degrees C. There was an increase in the recorded temperatures in the root canal for all three temperature settings with the mean temperature range from 38.52 degrees C to 61.58 degrees C. The mean temperature of the empty heating chamber was also measured and was accurately indicated on the control unit. However, the mean temperature of the gutta-percha in the heating chamber was almost 20 degrees C cooler than expected at each of the three settings. Finally, there was more than a 100 degrees C decrease in the mean temperature of the extruded gutta-percha in relation to the temperature of the gutta-percha in the heating chamber. Several clinically relevant observations were noted. Each of these observations was related to the temperature setting of the Obtura II control unit.