ABSTRACT
The cellular levels of the three translational initiation factors, IF1, IF2, and IF3, increase as a function of growth rate in parallel with those of ribosomes. Therefore both ribosomal and initiation factor gene expression is under metabolic control. To address how expression of the Escherichia coli gene for IF1, infA, is regulated, a 3-kilobase region of the genome surrounding infA was sequenced. The 5' and 3' termini of in vivo infA transcripts were defined by S1 nuclease mapping, and mRNA size was measured by Northern blot hybridization. The infA gene is transcribed by two promoters, P1 and P2, which generate transcripts of 525 and 330 nucleotides, apparently ending at the same rho-independent terminator. Analyses of operon and protein fusions to lacZ demonstrate that neither infA transcription nor translation is affected by high cellular levels of IF1. However, P2, but not P1, increases in activity as a function of the growth rate of the cell and is the dominant promoter in rich medium. Therefore, metabolic control of infA expression occurs exclusively at the level of transcription by the P2 promoter.
Subject(s)
Escherichia coli/genetics , Eukaryotic Initiation Factor-1/genetics , Gene Expression Regulation, Bacterial , Operon , Amino Acid Sequence , Base Sequence , Blotting, Northern , Cloning, Molecular , DNA , Escherichia coli/growth & development , Escherichia coli/metabolism , Eukaryotic Initiation Factor-1/metabolism , Gene Expression , Kinetics , Molecular Sequence Data , Promoter Regions, Genetic , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Restriction Mapping , Transcription, Genetic , beta-Galactosidase/geneticsABSTRACT
Calcium hydroxide is a material which has been used for a variety of purposes since its introduction into dentistry in the early part of the twentieth century. In its pure form, the substance has a high pH, and its dental use relates chiefly to its ability to stimulate mineralization, and also to its antibacterial properties. A range of products has been formulated with different therapeutic actions, the effects of which are partially dependent upon the tissue to which they are applied. The material is reviewed under the following general headings: biochemical actions; dental formulation; uses.
Subject(s)
Calcium Hydroxide , Dentin, Secondary/chemically induced , Root Canal Filling Materials , Calcium Hydroxide/chemistry , Calcium Hydroxide/pharmacology , Dental Pulp Capping , Humans , Pulpotomy , Root Resorption/prevention & control , Tooth RemineralizationABSTRACT
The efficacy of low temperature (70 degrees C) thermoplasticized gutta-percha used to seal root canals by the retrograde approach following apicectomy was assessed. A dye leakage technique was used, and gutta-percha was compared with amalgam. Two groups of different sized roots were apicected, and their root canals instrumented and filled conventionally with laterally condensed gutta-percha. Each group was randomly divided into four sub-groups; one was the control group in which no further treatment was carried out. In the other three groups the apical 3 mm of gutta-percha was removed, and the apical cavities filled as follows: group I with 70 degrees C thermoplasticized gutta-percha with sealer; group II with 70 degrees C thermoplasticized gutta-percha without sealer; group III with amalgam. The roots were rendered transparent by acid demineralization, and maximum dye penetration was measured. The results showed statistically significant ranking of leakage between the four sub-groups: 70 degrees C thermoplasticized gutta-percha with sealer less than 70 degrees C thermoplasticized gutta-percha without sealer less than amalgam less than control. The larger canals in all four sub-groups also exhibited significantly greater leakage than the smaller ones.
Subject(s)
Gutta-Percha , Retrograde Obturation/methods , Cold Temperature , Dental Amalgam , Dental Leakage/prevention & control , Evaluation Studies as Topic , Humans , Root Canal Filling MaterialsABSTRACT
An analog type apex locator was used to check the position of dentine pins. The teeth restored with the pins were reviewed. The analog type apex locator was easy to use and the readings obtained correlated well with the presence or absence of later symptoms from the tooth. This electrical method of checking pin position was more discerning than the method of direct observation.
Subject(s)
Dental Instruments , Dental Pins , Tooth/anatomy & histology , Evaluation Studies as Topic , HumansABSTRACT
There is considerable variation in the composition of primary and secondary dentine. In general, secondary deposits, regardless of type, contain less calcium, phosphorous, and collagenous matrix per unit volume when compared to primary dentine. Fluoride levels show the reverse tendency. These observations suggest a more open, porotic structure for secondary deposits.
