Demand for and utilization of dental services among Hong Kong employees with and without dental benefit coverage

The objectives of the present study were to investigate the effects of employer-provided dental benefits on the pattern of demand for and utilization of dental services among Hong Kong employees and to analyse whether employees' awareness about an existing dental benefit programme influenced their dental service demand and utilization. Staff from 11 selected companies with and without dental benefits responded to questionnaires concerning their personal factors, demand for dental services, and utilization of dental services and about their awareness of their dental benefit coverage. Overall response rate was 67%. The socio-demographic characteristics of those respondents who were covered and those who were not were similar. Forty per cent of the covered respondents were not aware of their dental benefit coverage, so analysis was performed with three groups of respondents, covered and aware, covered and unaware, and uncovered. A larger proportion of employees in the "aware" group had visited a dentist in the previous 12 months and had visited a dentist for asymptomatic reasons. The "aware" group reported more "low expenditure" items and less "high expenditure" items. Those who were aware of their dental benefit coverage irrespective of the type of scheme reported a significantly higher demand than those who were not aware of their coverage. Demand and utilization of the covered, but unaware, group was more similar to the uncovered group than to the "aware" group. Coverage per se had no apparent effect on the demand for dental services. Further studies will be necessary to establish that higher dental care demand and utilization induced by third party schemes also leads to improved oral health.

[Multiple chemical sensitivity disorder in patients with neurotoxic illnesses]

The data of 466 subjects suffering from neurologic disorders which are suggested to be caused by neurotoxic agents in their environment retrospectively was evaluated and documented. Among these cases there were 151 subjects with symptoms of Multiple Chemical Sensitivity Disorder (MCSD). The relationship between the neurological health impairments and neurotoxic agents in the environment of these patients was characterised using five different categories (probable = A, possible = B, uncertain = C, unclarified = D, not probable = E). From the 466 patients 320 subjects (69%) could be assigned to the categories A and B, respectively. Within theses 320 cases with chronic neurotoxic health impairments 136 subjects (79 females and 57 males) showed signs of MCSD. Age and gender of cases as well as duration and character of exposure to neurotoxic substances retrospectively were assessed from the explicit files of the patients, which had been made anonymous for this purpose. Frequency of characteristic symptoms of neurotoxicity were analysed. Results are given for patients with neurotoxic health impairments with MCSD (n = 136) and without MCSD (n = 184). Neurotoxic substances which were used as indoor wood preservatives (mainly Pentachlorophenol and/or Lindane) were found to be the causative agents in 63% of the cases with neurotoxic health impairments and MCSD. Other important neurotoxic substances to which the patients were mainly exposed were organic solvents (25%), formaldehyde (15%), dental materials (15%), pyrethroides (13%), and other biocides (19%) (multiple exposures were possible). The time of exposure was calculated as being > or = 10 years for 55% of the patients with MCSD and for 50% of the group with neurotoxic health impairments but without MCSD. Out of the 184 cases with neurotoxic health impairments but without MCSD there were 22%, and out of the 136 cases with MCSD there were 39% who showed all symptoms of chronic fatigue syndrome. 53% of the cases with MCSD had an allergic disposition compared to only 20% of the cases without MCSD. This work is not a controlled epidemiological study but a retrospective documentation and evaluation of data related to environmental medicine. With the present documentation in this purely descriptive manner the proof of a causal relationship was not possible or intended. But because corresponding epidemiological studies are lacking, this documentation can give important information on characteristic features of Multiple Chemical Sensitivity Disorder and chronic neurotoxic health impairments. Such information is essential for planning and carrying out epidemiological studies urgently needed in this field.

Dental hygienists in Hong Kong: present and future status

PURPOSE

This study assessed the current employment status of dental hygienists practicing in Hong Kong, investigated factors affecting their employment, evaluated the satisfaction of local dental hygienists and their employers, and explored the career prospects of dental hygienists in Hong Kong.

METHODS

All registered dental hygienists (n = 64), all dentists who employed dental hygienists (n = 25), and a systematic sample of dentists who did not employ dental hygienists (n = 278) were surveyed in June 1994 concerning employment situation, salaries, job satisfaction, and opinions on future prospects for dental hygienists.

RESULTS

Response rates were 86% for dental hygienists (n = 55), 88% for employers (n = 22), and 63% for dentists at large (n = 175). Among the dental hygienists, 87% still were employed as dental hygienists, and both the dental hygienists and their employers agreed that the employment situation was satisfactory; however, several dental hygienists were considered to be working below their level of qualification. Major reasons for dentists not to employ a dental hygienist were having only one operatory and having an inadequate number of patients. In general, employers expressed satisfaction with the performance of the dental hygienists. Major reasons for employing a dental hygienist were that a dental hygienist would add professional and economical benefit to their clinic. Few dentists would support expanded duties for dental hygienists.

CONCLUSIONS

In Hong Kong, dental hygienists and their employers comprise a small group with limited impact on oral healthcare services. Dental hygienists' perceptions of their future roles and ambitions are higher than those of their employers. To further the development of dental services in Hong Kong and meet documented oral healthcare needs in the population, greater utilization of dental hygienists should be promoted.

Role of the mitochondrial DnaJ homologue, Mdj1p, in the prevention of heat-induced protein aggregation

The role of the mitochondrial Hsp70 system in the prevention of heat-induced protein aggregation was studied in isolated mitochondria from Saccharomyces cerevisiae. Firefly luciferase was employed as a thermolabile tester protein. After shift to 40 degrees Celsius transient increase of mt-Hsp70/luciferase complex was observed, which required functional Mdj1p and Mge1p, the mitochondrial homologues of DnaJ and GrpE. The kinetics of luciferase aggregation, however, were not influenced by mutations in either mt-Hsp70 or Mge1p. Only the absence of Mdj1p led to enhanced protein aggregation. Thus, a central role in the transient protection against heat stress is attributed to this mitochondrial DnaJ homologue.

Changes in utilization and cost sharing within the Danish National Health Insurance dental program, 1975-90

The aims of the analysis were 1) to examine the development in utilization of dental care provided for adults in Denmark under the National Health Insurance during the period 1975-90; 2) to assess the appropriateness of available dental care statistics for studies of oral health trends; and 3) to analyze the price development of dental services during 1975-90 and its impact on patient and Insurance expenses, respectively. Utilization and economic data were retrieved from available registers and analyzed. Three trends were found. First, the utilization has increased more than what could be explained by the population increase; secondly, the panorama of dental services changed from predominantly restorative/extraction services to predominantly diagnostic/preventive services. Thirdly, the price paid by Danish adults for dental care increased disproportionately to other price developments in society. On the basis of traditional health economic theory this development could be expected to affect demand for dental services negatively.

Changes in demand for dental care among Danish adults, 1975-90

The aims of this study were 1) to analyze changes in and determining factors for demand for dental care among Danish adults during 1975-90, and 2) to apply standard cohort analysis on sequential cross-sectional survey data, thereby enabling the separation and examination of age, period, and cohort effects. Samples of non-institutionalized Danes aged 15 years and more were interviewed in 1975 (n = 1204), 1980 (n = 1108), 1985 (n = 1123), and 1990 (n = 1003), in accordance with a standardized questionnaire. Overall demand for dental care increased from 59% in 1975 to 76% in 1990; the younger the respondents, the higher the demand. Standard cohort table analysis indicated that the main effect derived from cohort succession; that is, the higher demand of the new cohorts entering the population remained higher than that of previous cohorts. Logistic regression analysis indicated that from 1980 to 1990 the significant predictors for regular dental care shifted from being predominantly predisposing and need variables to predominantly enabling and need variables.

[Post-traumatic aneurysma spurium of the subclavian artery]

In peacetime, injuries to the subclavian artery are now very rare. Even more rare are posttraumatic aneurysms and indirect damage to the brachial plexus as a result of injury. The clinical findings, diagnosis and treatment of such a case are described and discussed. Consideration of all the clinical symptoms as a whole is of the outmost importance in the diagnostic process. The development of neurological symptoms in the course of injury with a topographic relationship to the corresponding anatomical structures gave rise to the preliminary diagnosis in this particular case. CT and DSA confirmed the diagnosis. Although surgical treatment is urgently indicated in such cases, resection of the aneurysm as an elective surgical procedure was preferred.

Polyvinylidene fluoride monofilament sutures: can they be used safely for long-term anastomoses in the thoracic aorta?

Polyvinylidene fluoride (PVDF) represents an attractive alternative to polypropylene as a monofilament vascular suture because of its satisfactory physicochemical properties, it ease of handling, and its good biocompatibility. However, the polymer's ability to remain mechanically and chemically stable when exposed to a mild hydrolytic environment over the long term has yet to be demonstrated. One in vitro study involved the comparison of the long-term relative resistance of PVDF and polypropylene sutures to hydrolysis for a period of 9 years. The PVDF suture showed major molecular rearrangements from the original ratio of three crystalline structures to the single beta crystalline phase. The observation of some surface oxidation and water inhibition did not significantly modify the tensile strength of the PVDF suture, which retained 92.5% of its original value. In contrast, the polypropylene sample did not undergo any recrystallization but was associated with more oxidation byproducts and more water molecules near the surface, which contributed to a 46.6% loss in initial tensile strength. An in vivo study confirmed that PVDF sutures are biocompatible and are able to maintain satisfactory biostability when used to anastomose thoracic aortic allografts for a period of 6 months in the dog. The cellular reaction of fresh allografts as well as the control autografts to PVDF sutures was minimal. In other allografts that had been preserved in a supplemented medium for 1 week prior to implantation, the PVDF sutures healed satisfactorily with the formation of neocollagen and few macrophages surrounding the monofilament. No evidence of instability at the allograft-host artery junction was observed, confirming that the PVDF sutures were able to ensure a secure anastomosis in the thoracic aorta. PVDF sutures have demonstrated superior long-term biostability in vitro and minimal tissue response in vivo. These are two essential requirements when evaluating the use of a suture for vascular surgery in general and thoracic aortic surgery in particular.

The role of the GrpE homologue, Mge1p, in mediating protein import and protein folding in mitochondria

Mge1p, a mitochondrial GrpE homologue, has recently been identified in the yeast Saccharomyces cerevisiae and a role for this protein in precursor import has been reported. To dissect the molecular mechanism of Mge1p function, conditional mge1 mutants were constructed. Cells harbouring mutant mge1 accumulated precursor proteins at restrictive temperature. Both kinetics and efficiency of import were reduced in mitochondria isolated from strains possessing mutant mge1. Binding of mitochondrial-Hsp70 (mt-Hsp70) to incoming precursor proteins was abolished at restrictive temperature. Nucleotide-dependent dissociation of mt-Hsp70 from the import component MIM44 was reduced in mitochondria from mutant mge1 strains. Furthermore, at restrictive temperature an increase of incompletely folded, newly imported protein and enhanced protein aggregation was observed in mitochondria isolated from the mutant strains. We conclude that Mge1p exerts an essential function in import and folding of proteins by controlling the nucleotide-dependent binding of mt-Hsp70 to substrate proteins and the association of mt-Hsp70 with MIM44.

Sorting of cytochrome b2 to the intermembrane space of mitochondria. Kinetic analysis of intermediates demonstrates passage through the matrix

Precytochrome b2 is targeted to the mitochondrial intermembrane space by a dual targeting sequence comprising 80 amino acids. A kinetic analysis of intramitochondrial sorting was performed. The intermediate-size form accumulated transiently in the matrix. When import was performed in the presence of metal chelators to prevent the first processing by the matrix processing peptidase, > 40% of the imported precursor was localized in the matrix. A deletion of 13 amino acids in the intermembrane space sorting sequence caused partial inhibition of the first processing, and a transient accumulation of the precursor form in the matrix was also observed. The decrease in this matrix-localized precursor form paralleled an increase in the mature-size form in the intermembrane space. A point mutation in the mitochondrial targeting sequence (N-terminal to the sorting sequence) resulted in missorting to the matrix space. Furthermore, a chimeric protein consisting of the initial 85 residues of cytochrome b2 fused to dihydrofolate reductase was partially targeted to the matrix at 15 degrees C, but not at 25 degrees C. Together, the results presented here indicate that cytochrome b2 passes through the matrix on its sorting pathway to the intermembrane space.

Dental anxiety in Danish and Chinese adults--a cross-cultural perspective

The aim of this study was to correlate dental anxiety as reported by two different ethnic groups with socio-demographic factors, dental status, and dental behaviour. Two randomly selected populations aged 35-44 years and 65-74 years were interviewed. The populations comprised 214 and 99 Danes and 384 and 497 Hong Kong Chinese respectively. Dental anxiety was assessed by the Corah Dental Anxiety Score (DAS). Mean DAS scores were significantly higher in Chinese than in Danes (8.7-10.3 and 6.7-8.2, respectively) and higher in the younger than in the older groups. Moderate to phobic dental anxiety was reported by 15% of the Danes and 30% of the Chinese, the latter proportion far beyond what is usually reported in Western populations. Only in the Chinese group did women report more anxiety than men. Regression analysis indicated that only a few of the variables selected to explain anxiety determinants had significant explanatory value. Among Chinese, gender was the most predominant in both age groups followed by perceived condition of teeth in the younger age group. Among Danes, perceived condition of teeth had an explanatory value for both age groups and dental visit pattern was the strongest for the younger age group. In spite of statistical significance, all explanatory values were small and indicate that variables not included in this analysis may exert a greater influence on the variation in dental anxiety. DAS, seemingly, was able to highlight variations in dental anxiety in the populations in spite of their differences and made interpretations feasible with regard to contrasting dental care behaviour and dental status.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral health and dental care in Hong Kong

With a population of six million people and situated at the South-eastern corner of mainland China, Hong Kong is considered as the gateway between East and West, often playing a role disproportionate to its territorial or population size. The FDI World Dental Congress 1995 provides an impetus to familiarise colleagues worldwide with the oral health and dental care situation in Hong Kong. Water fluoridation was introduced in 1961, which has achieved a continuous low and stable caries prevalence in children as well as in adults. Edentulousness among adults is usually not apparent until after age 55, but at much lower rates than in comparable western industrialised populations. Periodontal conditions in adults are dominated by calculus and shallow pockets. Overall, treatment needs are mainly oral hygiene and simple restorative treatment. Dental awareness is considered low with only a minority of the population seeking dental care on a regular basis. Traditional Chinese health beliefs are common and may influence health behaviour in terms of self- or professional care. Dental care is mainly provided by around 1000 private dental practitioners but special government dental programmes are established for primary school children, who are mainly treated by dental therapists, and for civil servants and their dependents. Dental hygienists are trained in very limited numbers. Dental specialties are under development as part of a newly established Academy of Medicine. Developments are under way to introduce new preventive oriented programmes for pre-school and secondary school age groups.

Prevalence and structure of dental benefit schemes in Hong Kong

Before the impact of employer-provided dental benefit schemes on the dental care delivery system can be evaluated in Hong Kong, the prevalence of these schemes and their structures must be established. A mailed questionnaire survey was conducted of a representative group of companies with more than 100 employees (n = 495). Response rate to the mail survey was 38 per cent (n = 186). Non-respondents were stratified according to their nature of business and one third was randomly selected for a follow-up by telephone to which 84 per cent responded (n = 81). After adjustment, 16 per cent of companies of that size were found to be providing dental benefit schemes to their staff. The prevalence was related to the nature of business of the companies. Among companies providing dental benefits, administrators from selected companies were interviewed. It was found that dental benefit schemes could be broadly divided into two types: One characterised by cash-benefit and the other by service-benefit. Treatment items covered by the schemes were mostly simple services such as diagnostic items, simple restorations and simple extractions. The influence of these dental benefit schemes on the dental care-seeking behaviour of the beneficiaries is under investigation.

Subcellular relocalization of a long-chain fatty acid CoA ligase by a suppressor mutation alleviates a respiration deficiency in Saccharomyces cerevisiae

We have isolated an extragenic suppressor, FAM1-1, which is able to restore respiratory growth to a deletion of the CEM1 gene (mitochondrial beta-keto-acyl synthase). The sequence of the suppressor strongly suggests that it encodes a long-chain fatty acid CoA ligase (fatty-acyl-CoA synthetase). We have also cloned and sequenced the wild-type FAM1 gene, which is devoid of suppressor activity. The comparison of the two sequences shows that the suppressor mutation is an A-->T transversion, which creates a new initiation codon and adds 18 amino acids to the N-terminus of the protein. This extension has all the characteristics of a mitochondrial targeting sequence, whilst the N-terminus of the wild-type protein has none of these characteristics. In vitro mitochondrial import experiments show that the N-terminal half of the suppressor protein, but not of the wild-type, is transported into mitochondria. Thus, we hypothesize that the suppressor acts by changing the subcellular localization of the protein and relocating at least some of the enzyme from the cytosol to the mitochondria. These results support the hypothesis that some form of fatty acid synthesis, specific for the mitochondria, is essential for the function of the organelle.

Chinese health beliefs and oral health practices among the middle-aged and the elderly in Hong Kong

The purpose of this paper was to study possible relationships between traditional Chinese health beliefs and health practices in adult Chinese in a modernized society. The study populations comprised 398 35-44-yr-old and 559 65-74-yr-old Hong Kong Chinese. The respondents were categorized into three groups with weak, moderate, or strong Chinese beliefs on the basis of interview questions on the causes of gum disease. Chinese preventive practices and Chinese pain practices were defined according to respondents' reported use of recommended traditional cures. Questions on generally accepted oral practices were phrased in terms of frequency of daily brushing of teeth, use of toothpicks the previous day, and whether or not teeth were flossed the previous day. Around one-third of the respondents had weak, almost one-half had moderate, and around one-quarter expressed strong Chinese health beliefs. No significant differences in Chinese health beliefs were found between men and women in either age group, or between the age groups. In the 35-44 age group, more of those with a higher education were in the "weak" Chinese health belief category, whereas, conversely, more of those with a lower education expressed stronger Chinese health beliefs (P < 0.05). Women in both age groups reported significantly more frequent brushing. Toothpicks were used by around three-quarters of both age groups, but flossing was extremely rare.(ABSTRACT TRUNCATED AT 250 WORDS)

Tooth and root conditions in the middle-aged and the elderly in Hong Kong

In an oral health survey of Hong Kong Chinese conducted in 1991, a sample of 372 35-44-yr-olds and 537 noninstitutionalized 65-74-yr-olds were interviewed and clinically examined. The examination procedures, instruments, and diagnostic criteria used to detect coronal caries followed those recommended by the World Health Organization (1987). The diagnostic criteria used to assess root-surface caries were based on those used in a national oral health survey of US employed adults (National Institute of Dental Research, 1987). Calibration of examiners was conducted before the survey and the interexaminer reliability was found to be very high; the kappa statistics were 0.93 and 0.91 for the younger and older age groups, respectively. None of the 35-44-yr-olds were edentulous and 96% had 21 teeth or more. The prevalence of edentulousness among the elderly was 12%. The DMFT indices of the younger and older age groups were 8.7 and 18.9, respectively. In both age groups, MT was the major component of the DMFT index, and female subjects had a slightly higher score. The prevalences of decayed/filled roots were 7% and 26% for the 35-44- and 65-74-yr-olds, respectively. As compared with previous surveys conducted in Hong Kong, there has been a 40% reduction in the DMFT index of the 35-44-yr-olds since 1968, but little change in the tooth and root conditions was noted between 1984 and 1991.

Use of dental services by the middle-aged and the elderly in Hong Kong

The objectives of this analysis were to describe the dental service use pattern of the 35-44- and 65-74-yr-old age groups and to determine to what extent this pattern could be explained by selected sociodemographic and attitudinal variables. The study populations comprised 398 35-44-yr-old and 559 65-74-yr-old Hong Kong Chinese. Use of dental services was determined on the basis of the respondents' own perception of the regularity of their dental visits and by the time since the last dental visit. The younger groups was categorized into regular users, irregular users, and nonusers, and the older group was categorized into three groups according to last dental visit (within 2 yr, 2-5-yr, 5 yr or more). A modification of the Andersen and Newman model for individual determinants of health care use was used as the framework for a logistic regression analysis. Predisposing variables were sex, education, occupation, attitudes, knowledge, preventive orientation, and dental anxiety; enabling variables were Family Possession Index, income, family support and access to a dental programme; need variables were perceived conditions of teeth, dental problems, dental pain, need for treatment, normative need for treatment, and denture wearing. In general, use of dental services was low. For the 35-44-yr-olds, the best regression model (sensitivity: 62%, specificity: 95%, overall correct classification: 88%) indicated that there was an increased probability of having a regular dental care pattern if respondents were prevention oriented, had access to a dental benefit programme, had not experienced pain, had a higher income, perceived their teeth as fair or poor, and perceived a need of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The Hong Kong adult oral health survey--1991: background, study population, and methods

This second adult oral health survey was conducted with the following main aims: 1) to describe the oral health conditions and to analyse the oral health care needs and demands of 65-74-yr-olds in Hong Kong, and to propose appropriate strategies for meeting their needs in the light of societal obligations; 2) to describe the oral health conditions and to analyse the oral health care needs and demands of 35-44-yr-olds in Hong Kong with special emphasis on assessment of changes in this age group since 1984 (when the first adult oral health survey was conducted); 3) to assess the impact of sociodemographic and dental care system factors on the oral health status of selected adult age groups: and 4) to utilize survey data to refine curriculum development and research strategies in the Faculty of Dentistry, as well as in the proposal of appropriate action to governmental committees on dental health policy. For enhanced comparability with the previous study, the 35-44-yr-olds were selected from the same geographic areas of Hong Kong Island. Multistage cluster sampling was used to recruit the study population, defined geographic units and addresses being used as the starting-point. A sample of 398 subjects was selected, of whom 93% were both interviewed and clinically examined. The 65-74-yr-olds were recruited from housing estates in all principal areas of Hong Kong, yielding a sample of 559 subjects, of whom 96% were both interviewed and clinically examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental health knowledge and attitudes among the middle-aged and the elderly in Hong Kong

Previous studies on adult Hong Kong Chinese have indicated that their level of knowledge of and attitudes toward dental health might be a potential barrier to effective oral preventive efforts. The knowledge and attitudes of elderly Chinese have not previously been studied. The objectives of this study were to describe Hong Kong adults' knowledge of the causes of the two main oral diseases, caries and periodontal disease, and possible preventive measures, and to analyse possible relationships between knowledge and attitudes and selected sociodemographic and utilization variables. Two populations aged 35-44 yr (n = 398) and 65-74 yr (n = 559) were selected for the study, which was conducted as structured interviews. A knowledge score was constructed from questions on caries and periodontal disease development and prevention. Attitudes were measured in the younger group by beliefs and evaluations of those beliefs according to the theory of reasoned action (the higher the score, the more positive the attitude). Knowledge scores were almost normally distributed in the younger respondents, but were heavily skewed toward 0 in the older group. In both age groups, increased level of education and regularity or recency of dental visits were strongly associated with dental knowledge. Women, regular dental care users, and prevention-oriented respondents had higher attitude scores. There was no correlation between knowledge and attitudes. Some improvement in knowledge seems to have taken place, especially on the cause of caries, with fewer 35-44-yr-old respondents claiming lack of knowledge of the causes of caries and gum disease than in a previous study.(ABSTRACT TRUNCATED AT 250 WORDS)

Attitudes toward dentists and the dental care system among the middle-aged and the elderly in Hong Kong

A sample of 398 35-44-yr-old and 559 65-74-yr-old Hong Kong Chinese were interviewed by trained interviewers using a structured questionnaire in an oral health survey conducted in 1991. The present analysis aimed to describe the dental-care-seeking behaviour and attitudes of these subjects. It was found that 43% of the younger and 23% of the older age group had visited a dentist within the past year. More than half of the elderly and a quarter of the adults had not been to a dentist for 3 yr or more, and the main reason given by these subjects was that they felt that nothing was wrong. The vast majority of the subjects consulted a dentist only when they had toothache or other dental problems. Less than 20% of the 35-44-yr-olds visited a dentist for a check-up or teeth cleaning, and these subjects were described as having a prevention-oriented attitude toward oral care. The result of a logistic regression analysis showed that there was a higher chance for subjects to have this attitude if they had dental programme coverage, perceived their teeth to be good, had better dental health knowledge, had a more positive dental attitude, and were less anxious about dental care. However, the influence of these factors was quite weak, because the overall percentage of correct classification of the model was 83.7% and the sensitivity was only 23.3%.

Mitochondrial protein import: mechanisms, components and energetics

The transport of nuclear-encoded proteins from the cytosol into mitochondria is mediated by targeting (signal) sequences present on precursor forms. Most precursors of the mitochondrial matrix possess amino-terminal signals which characteristically contain hydroxylated and basic amino acids and lack acidic residues. With a minority of precursor proteins, internal sequence motifs can direct proteins to the mitochondria (Pfanner, N., Hoeben, P., Tropschug, M. and Neupert, W. (1987) J. Biol. Chem. 262, 14851-14854). The presence of a mitochondrial targeting sequence alone, however, is not sufficient for specific targeting to the organelle and further to the various subcompartments. There is the need for components which recognise the targeting sequences and others which keep the precursor protein in a translocation-competent form. Beyond the recognition step, components are required which mediate translocation across the mitochondrial membranes. Mitochondria posses two translocation machineries, one in the outer membrane and one in the inner membrane. The matrix space harbors a number of factors which participate in the import of proteins, in their unfolding and folding. Energy is required at several steps of these processes.

XDJ1, a gene encoding a novel non-essential DnaJ homologue from Saccharomyces cerevisiae

The gene encoding a novel DnaJ-like protein, termed Xdj1, has been identified by amplification of Saccharomyces cerevisiae genomic DNA. An open reading frame of 1380 bp was detected. Disruption of XDJ1 did not yield any detectable new phenotype. A double-deletion strain containing a disruption of both XDJ1 and YDJ1, another gene coding for a DnaJ-like protein, was still viable. Under a variety of growth conditions, no XDJ1 transcripts could be detected by Northern blot analysis and no translation product was found by immunoblotting with antibody against Xdj1 produced in Escherichia coli. Thus, XDJ1 is either expressed only under very specific conditions or represents a silent gene.