[Gender-related differences in working practice and professional growth of dentists]

The paper presents some aspects of professional growth, continuous education and working conditions of female dentists having impact on treatment quality and dental service state in general. Questionnaire survey was carried out in 124 dentists, both male and female, aged 22 to 60 years. The study revealed gender asymmetry influencing their competitive ability, physical and emotional well-being.

Peculiarities of the Regulation of Gene Expression in the Ecl18kI Restriction–Modification System

Transcription regulation in bacterial restrictionmodification (RM) systems is an important process, which provides coordinated expression levels of tandem enzymes, DNA methyltransferase (MTase) and restriction endonuclease (RE) protecting cells against penetration of alien DNA. The present study focuses on (cytosine-5)-DNA methyltransferase Ecl18kI (M.Ecl18kI), which is almost identical to DNA methyltransferase SsoII (M.SsoII) in terms of its structure and properties. Each of these enzymes inhibits expression of the intrinsic gene and activates expression of the corresponding RE gene via binding to the regulatory site in the promoter region of these genes. In the present work, complex formation of M.Ecl18kI and RNA polymerase from Escherichia сoli with the promoter regions of the MTase and RE genes is studied. The mechanism of regulation of gene expression in the Ecl18kI RM system is thoroughly investigated. M.Ecl18kI and RNA polymerase are shown to compete for binding to the promoter region. However, no direct contacts between M.Ecl18kI and RNA polymerase are detected. The properties of M.Ecl18kI and M.SsoII mutants are studied. Amino acid substitutions in the N-terminal region of M.Ecl18kI, which performs the regulatory function, are shown to influence not only M.Ecl18kI capability to interact with the regulatory site and to act as a transcription factor, but also its ability to bind and methylate the substrate DNA. The loss of methylation activity does not prevent MTase from performing its regulatory function and even increases its affinity to the regulatory site. However, the presence of the domain responsible for methylation in the M.Ecl18kI molecule is necessary for M.Ecl18kI to perform its regulatory function.

Peculiarities of the Regulation of Gene Expression in the Ecl18kI Restriction-Modification System

Transcription regulation in bacterial restriction-modification (R-M) systems is an important process, which provides coordinated expression levels of tandem enzymes, DNA methyltransferase (MTase) and restriction endonuclease (RE) protecting cells against penetration of alien DNA. The present study focuses on (cytosine-5)-DNA methyltransferase Ecl18kI (M.Ecl18kI), which is almost identical to DNA methyltransferase SsoII (M.SsoII) in terms of its structure and properties. Each of these enzymes inhibits expression of the intrinsic gene and activates expression of the corresponding RE gene via binding to the regulatory site in the promoter region of these genes. In the present work, complex formation of M.Ecl18kI and RNA polymerase from Escherichia сoli with the promoter regions of the MTase and RE genes is studied. The mechanism of regulation of gene expression in the Ecl18kI R-M system is thoroughly investigated. M.Ecl18kI and RNA polymerase are shown to compete for binding to the promoter region. However, no direct contacts between M.Ecl18kI and RNA polymerase are detected. The properties of M.Ecl18kI and M.SsoII mutants are studied. Amino acid substitutions in the N-terminal region of M.Ecl18kI, which performs the regulatory function, are shown to influence not only M.Ecl18kI capability to interact with the regulatory site and to act as a transcription factor, but also its ability to bind and methylate the substrate DNA. The loss of methylation activity does not prevent MTase from performing its regulatory function and even increases its affinity to the regulatory site. However, the presence of the domain responsible for methylation in the M.Ecl18kI molecule is necessary for M.Ecl18kI to perform its regulatory function.

[Differential approach to spring water choice regarding fluoride content for caries prevention]

The research includes an investigation of the tap water in different districts of Moscow. It was found out that Moscow tap water contains little fluoride, the difference between districts and okrugs is of no consequence. There is no centralized water fluoridization in Moscow therefore the authors suggest using bottled potable water with sufficient fluoride level. The fluoride concentration in one hundred of the most popular and wide-spread bottled potable water labels was examined. High in fluoride and low in fluoride labels were identified as well as the labels with the optimal fluoride content. Some practical guidelines for selection of bottled potable water depending on the quantity of liquid consummation were elaborated.

[Secondary structure of SsoII-like (cytosine-5)-DNA methyltransferases N-terminal region determined by circular dichroism spectroscopy]

(Cytosine-5)-DNA methyltransferase SsoII (M.SsoII) has a long N-terminal region (1-71 residues) preceding the sequence with conservative motifs, which are characteristic for all DNA methyltransferases of such kind. The presence of this region provides M.SsoII capability to act as a transcription regulator in SsoII restriction-modification system. To perform its regulatory function, M.SsoII binds specifically to a 15-mer inverted repeat in the promoter region of SsoII restriction-modification system genes. In the present work, properties of the protein delta(72-379)M.Ecl18kI are studied, which is a deletion mutant of the SsoII-like DNA-methyltransferase M.Ecl18kI and is homologous to M.SsoII N-terminal region. delta(72-379)M.Ecl18kI capability to bind specifically a DNA duplex containing the regulatory site is demonstrated. However, such a binding takes place only in the presence of high protein excess relative to DNA, which could indicate an altered structure in the deletion mutant in comparison with the full-length M.SsoII. Circular dichroism spectroscopy demonstrated that delta(72-379)M.Ecl18kI has a strongly pronounced secondary structure and contains 32% a-helices and 20% beta-sheets. Amino acid sequences alignment of M.SsoII N-terminal region and transcription factors of known spatial structure is made. An assumption is made how alpha-helices and beta-sheets are arranged in M.SsoII N-terminal region.

[Factors influencing major stomatological diseases prevalence in student youth of Moscow city]

A clinical stomatological and social research of 432 young people at the age of 16-25 years was wade in establishments for higher and specialized secondary education in Moscow. It was found out that unbalanced food dominated by soft carbohydrates, frequent eating of sweets as well as low medical culture, lack of sanitary and hygienic knowledge and skills, negligence of preventive control contribute greatly to progression of caries and paradontal diseases. Bad habits and unheavy somatic affections do not have time early in life to exhibit their bad influence on teeth but they can violate the paradont.

[Stomatological dispensary treatment of students of Moscow higher educational establishments and ways of its improvement]

As a result of clinical epidemiological survey of 432 Moscow students and of evaluation of medical records of annual dental examination, the high-level of various pathologies of dentitions and low efficiency of annual examination were found out in 232 students. It was traced back that main faults of dental examination of students were: poor coverage by medical examinations; occasional nature of examinations; incomplete revelation of pathologies; lack of remedial measures and educative activities.

SsoII-like DNA-methyltransferase Ecl18kI: interaction between regulatory and methylating functions

The interaction of DNA-methyltransferase Ecl18kI (M.Ecl18kI) with a fragment of promoter region of restriction-modification system SsoII was studied. It is shown that dissociation constants of M.Ecl18kI and M.SsoII complexes with DNA ligand carrying a regulatory site previously characterized for M.SsoII have comparable values. A deletion derivative of M.Ecl18kI, Delta(72-379)Ecl18kI, representing the N-terminal protein region responsible for regulation, was obtained. It is shown that such polypeptide fragment has virtually no interaction with the regulatory site. Therefore, the existence of a region responsible for methylation is necessary for maintaining M.Ecl18kI regulatory function. The properties of methyltransferase NlaX, which is actually a natural deletion derivative of M.Ecl18kI and M.SsoII lacking the first 70 amino acid residues and not being able to regulate gene expression of the SsoII restriction-modification system, were studied. The ability of mutant forms of M.Ecl18kI incorporating single substitutions in regions responsible for regulation and methylation to interact with both sites of DNA recognition was characterized. The data show a correlation between DNA-binding activity of two M.Ecl18kI regions-regulatory and methylating.

[Prevalence of dental diseases among Moscow students and need of dentistry]

A clinical epidemiologic study was made among 432 Moscow students and as a part of it was found the high prevalence rate of pathologies of dentition and variety of nosologic forms. The most common cases were: caries, periodontal disease, deformity and anomalies of tooth position. These findings were necessary to estimate the need of all types of dentistry for Moscow students. It was specified that 43% of students were in need of filling and dental restoration, 35% were in need of crowns of tooth, 22% were in need of dental restoration by means of orthopedic constructions. Endodontic dentistry was necessary for 31% of students, surgical removal - for 8%, periodontal dentistry - for 37%.

[Synthesis and characteristics of modified DNA fragments containing thymidine glycol residues]

Chemical synthesis of a series of modified oligodeoxyribonucleotides containing one or two residues of thymidine glycol (5,6-dihydro-5,6-dihydroxythymidine), the main product of oxidative DNA damage, is described. The thermal stability of DNA duplexes containing thymidine glycol residues was studied using UV spectroscopy. Introduction of even one thymidine glycol residue into the duplex structure was shown to result in its significant destabilization. Data on the interaction of DNA methyltransferases and type II restriction endonucleases with DNA ligands containing oxidized thymine were obtained for the first time. Introduction of a thymidine glycol residue into the central degenerate position of the recognition site of restriction endonuclease SsoII was found to result in an increase in the initial hydrolysis rate of the modified duplex in comparison with that of the unmodified structure. The affinity of C5-cytosine methyltransferase SsoII for the DNA duplex bearing thymidine glycol was found to be twofold higher than for the unmodified substrate. However, such a modification of the DNA ligand prevents its methylation. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2008, vol. 34, no. 2; see also http://www.maik.ru.

[Regulation of gene expression in type II restriction-modification system]

Type II restriction-modification systems are comprised of a restriction endonuclease and methyltransferase. The enzymes are coded by individual genes and recognize the same DNA sequence. Endonuclease makes a double-stranded break in the recognition site, and methyltransferase covalently modifies the DNA bases within the recognition site, thereby down-regulating endonuclease activity. Coordinated action of these enzymes plays a role of primitive immune system and protects bacterial host cell from the invasion of foreign (for example, viral) DNA. However, uncontrolled expression of the restriction-modification system genes can result in the death of bacterial host cell because of the endonuclease cleavage of host DNA. In the present review, the data on the expression regulation of the type II restriction-modification enzymes are discussed.