Nonspecific DNA binding by P1 ParA determines the distribution of plasmid partition and repressor activities

The faithful segregation, or "partition," of many low-copy number bacterial plasmids is driven by plasmid-encoded ATPases that are represented by the P1 plasmid ParA protein. ParA binds to the bacterial nucleoid via an ATP-dependent nonspecific DNA (nsDNA)-binding activity, which is essential for partition. ParA also has a site-specific DNA-binding activity to the par operator (parOP), which requires either ATP or ADP, and which is essential for it to act as a transcriptional repressor but is dispensable for partition. Here we examine how DNA binding by ParA contributes to the relative distribution of its plasmid partition and repressor activities, using a ParA with an alanine substitution at Arg351, a residue previously predicted to participate in site-specific DNA binding. In vivo, the parAR351A allele is compromised for partition, but its repressor activity is dramatically improved so that it behaves as a "super-repressor." In vitro, ParAR351A binds and hydrolyzes ATP, and undergoes a specific conformational change required for nsDNA binding, but its nsDNA-binding activity is significantly damaged. This defect in turn significantly reduces the assembly and stability of partition complexes formed by the interaction of ParA with ParB, the centromere-binding protein, and DNA. In contrast, the R351A change shows only a mild defect in site-specific DNA binding. We conclude that the partition defect is due to altered nsDNA binding kinetics and affinity for the bacterial chromosome. Furthermore, the super-repressor phenotype is explained by an increased pool of non-nucleoid bound ParA that is competent to bind parOP and repress transcription.

Insufficient levels of the nrdAB-encoded ribonucleotide reductase underlie the severe growth defect of the Δhda E. coli strain

The ATP-bound form of the Escherichia coli DnaA replication initiator protein remodels the chromosomal origin of replication, oriC, to load the replicative helicase. The primary mechanism for regulating the activity of DnaA involves the Hda and β clamp proteins, which act together to dramatically stimulate the intrinsic DNA-dependent ATPase activity of DnaA via a process termed Regulatory Inactivation of DnaA. In addition to hyperinitiation, strains lacking hda function also exhibit cold sensitive growth at 30°C. Strains impaired for the other regulators of initiation (i.e., ΔseqA or ΔdatA) fail to exhibit cold sensitivity. The goal of this study was to gain insight into why loss of hda function impedes growth. We used a genetic approach to isolate 9 suppressors of Δhda cold sensitivity, and characterized the mechanistic basis by which these suppressors alleviated Δhda cold sensitivity. Taken together, our results provide strong support for the view that the fundamental defect associated with Δhda is diminished levels of DNA precursors, particularly dGTP and dATP. We discuss possible mechanisms by which the suppressors identified here may regulate dNTP pool size, as well as similarities in phenotypes between the Δhda strain and hda⁺ strains exposed to the ribonucleotide reductase inhibitor hydroxyurea.

Evidence for roles of the Escherichia coli Hda protein beyond regulatory inactivation of DnaA

The ATP-bound form of the Escherichia coli DnaA protein binds 'DnaA boxes' present in the origin of replication (oriC) and operator sites of several genes, including dnaA, to co-ordinate their transcription with initiation of replication. The Hda protein, together with the β sliding clamp, stimulates the ATPase activity of DnaA via a process termed regulatory inactivation of DnaA (RIDA), to regulate the activity of DnaA in DNA replication. Here, we used the mutant dnaN159 strain, which expresses the β159 clamp protein, to gain insight into how the actions of Hda are co-ordinated with replication. Elevated expression of Hda impeded growth of the dnaN159 strain in a Pol II- and Pol IV-dependent manner, suggesting a role for Hda managing the actions of these Pols. In a wild-type strain, elevated levels of Hda conferred sensitivity to nitrofurazone, and suppressed the frequency of -1 frameshift mutations characteristic of Pol IV, while loss of hda conferred cold sensitivity. Using the dnaN159 strain, we identified 24 novel hda alleles, four of which supported E. coli viability despite their RIDA defect. Taken together, these findings suggest that although one or more Hda functions are essential for cell viability, RIDA may be dispensable.

Osteoporosis and osseointegration of implants

According to medical literature, osteoporosis and related bone pathologies are increasing in epidemic proportions. The exact etiology of the disease is unknown, but hormonal, dietary, and genetic factors all contribute to the related loss of bone density. In the disease process, bone loss occurs throughout the body. Research indicates that the mandible and maxilla are affected, and show oral manifestations. There is no scientific data to contraindicate the use of two-step osseointegrated implants in osteoporotic individuals. The purpose of this article is to review the literature regarding osteoporosis and its relationship to oral bone loss.

The effect of applicant age, job level, and accountability on perceptions of female job applicants

We used simulated videotaped employment interviews to assess the effect of accountability on impressions of female job applicants. One hundred and twenty American undergraduates majoring in business and personnel related areas were informed that they would be participating in the pilot testing of a new employee placement technique. The age of the job applicant (25, 40, or 55 years), the position for which they were being considered (assistant director or director), and the degree to which subjects were made to feel accountable for their impressions of the applicant (low or high accountability) were manipulated, resulting in a 3 x 2 x 2 between-subjects design. The predicted interaction between accountability and applicant age applicant age was found on age-related adjective checklist items. Increasing the subjects' accountability produced more stereotypical impressions of all applicants, along with a tendency to attribute the applicant's behavior to dispositional factors.

Relationship of osteoporosis to excessive residual ridge resorption

There are many systemic factors which contribute to alveolar bone loss and decreased ability to tolerate dental prostheses. Osteoporosis should be considered as a possibility. Observation of the high numbers of osteoporotic fractures in the geriatric population serves to illustrate the scope of this problem. The condition of osteoporosis results in bone loss in the maxillae and mandible as well as in other bones of the body. It is highly feasible that the disease makes a strong contribution to the deterioration of the dental health in the geriatric patient. The American diet is too low in calcium and too high in phosphorus. Added to the high incidence of lactose intolerance, it is difficult to control the mineral content of a patient's diet by simple modification of eating habits. Dietary supplementation is a convenient and inexpensive alternative. Rampant residual ridge resorption is a multifactorial problem. It is part of the responsibility of the dentist to consider all factors involved in this state. The dentist would serve the patient well by working in conjunction with the patient's physician in the diagnosis and treatment of osteoporotic states. The dentist has much to gain in the systemic treatment of the "impossible denture patient," for it is the dentist who must endure the frustrations of treating such a patient.

Heavy metal retention in tissues of cattle fed high cadmium sewage sludge

A diet containing 11.5% (dry matter basis) of a moderately high Cd sewage sludge was fed to six Hereford steers for 106 days to simulate a high sludge intake from sludge-amended soils. At a mean live weight of 460 kg, the steers were slaughtered and liver, kidney, bone, muscle, lung, brain and spleen tissues were collected for heavy metal determinations; tissues were also collected at this time from six control steers fed the same diet with no sludge. The sludge-fed cattle consumed an average of 8.95 kg of diet dry matter/day and gained 1.13 kg/day. This feed intake was slightly higher, but the gain lower than that of control cattle. All gains were equal to those expected from intake of non-sludge diet components. This indicated that the sludge had approximately zero energy value and was acting as a dietary diluent. The sludge metal content (ppm, dry basis) was: Cd, 98; Hg, 18; Pb, 466; Cu, 1,733, and Zn, 1,733. Addition of sludge increased metal contents of the feedlot diet to 30 to 100 times that of the control. Retention of heavy metals in the total animal from sludge ingestion averaged .09%, .06% and .3% for Cd, Hg and Pb; no retention was noted from Cu and Zn. These low fractional retentions increased tissue Cd, Hg and Pb concentrations of liver and kidney tissues by five to 20-fold. Estimates of levels that would enter the human diet from average beef tissue consumption if all feedlot steers were fed sludge are presented for Cd, Hg and Pb. The data indicate that cattle are a moderately effective screen against the entry of these potentially toxic metals into the human diet.

The development of preschool children of heroin-addicted mothers: a controlled study

Disturbances of growth and behavior in infants and toddlers of women addicted to heroin during pregnancy have been reported in uncontrolled studies. In this study, 3- to 6-year-old children of heroin-addicted mothers were compared to three other groups matched for age, race, sex, birth weight, and socioeconomic status. Heroin-exposed children weighed less and were shorter than those in the comparison groups; 14% had a head circumference below the third percentile. Heroin-exposed children were rated by parents as less well adjusted than control children and they differed significantly in perceptual measures and on subtests of the Illinois Test of Psycholinguistic Abilities and McCarthy Scales of Children's Abilities relating to the process of organization. These findings suggest that chronic intrauterine exposure to heroin may affect growth and behavior as well as perceptual and learning processes in preschool children.