Age-adjusted survival curves with application in the Framingham Study

Kaplan-Meier curves provide descriptors of survival information for different subgroups within a data set. Investigators frequently use these figures for descriptive comparison of the effect of a particular measure upon survival. When subjects enter a study at different ages and age is associated with survival, it is often desirable to adjust survival information for age differences in the subgroups. This report discusses several methods for age-adjustment of survival curves, including direct age-adjustment and proportional hazard modelling with age as a covariate.

Tuberculosis surveillance of community hospital employees. A recommended strategy

OBJECTIVE AND METHODS

To suggest a cost-effective strategy with a high degree of surveillance for the transmission of tuberculosis infection to employees in community hospitals. We performed a cost-benefit analysis of tuberculin skin testing over a 4-year period. The setting was a community hospital in Bronx, NY. The subjects consisted of employees of the hospital who were categorized into high-risk employees defined as individuals who worked daily in patient care and low-risk employees defined as those not directly involved in patient care. All cases of tuberculin skin test conversion among employees were reviewed over a 4-year period. The departments involved, total number of employees, chest radiographic findings, and prophylaxis instituted were noted.

RESULTS

The number of employees who were screened over the past 4 years consisted of 897 in 1990, 857 in 1991, 1357 in 1992, and 1316 in 1993. The mean annual conversion rate was 1%, 1.5%, 1.7%, and 1.4% for the 4 years, respectively. Skin test conversions according to job description revealed that of the total number of conversions 42% were from the nursing staff, 6.2% among the physicians and residents, and 52% among the ancillary staff. There was no difference in conversion between medical and nonmedical services such as the gynecology and surgical floors.

CONCLUSION

Since tuberculin conversion rates of high-risk employees and those exposed to infectious tuberculosis cases have been low, we suggested a comprehensive strategy of 6-month tuberculin testing for high-risk employees and yearly testing for low-risk employees and eliminating boosting and repeated testing at 12 weeks in those exposed to infectious cases of tuberculosis.

Syncytial mutations in the herpes simplex virus type 1 gK (UL53) gene occur in two distinct domains

Syncytial (syn) mutants of herpes simplex virus cause cell fusion. Many syn mutations map to the syn1 locus, which has been identified with the gK (UL53) gene. In this work, the gK genes of eight syn mutants derived from the KOS strain were sequenced to identify residues and, possibly, domains important for the fusion activity of mutant gK. DNA sequencing showed that six mutants (syn30, syn31, syn32, syn102, syn103, and syn105) had single missense mutations in the gK gene. Two of these, syn31 and syn32, had identical mutations that caused the introduction of a potential site for N-linked glycosylation. syn31 gK was analyzed by in vitro translation and found to utilize the novel glycosylation site. Two other mutants, syn8 and syn33, had three mutations each, resulting in three amino acid substitutions in syn8 and two substitutions in syn33. Of the 10 gK syn mutant sequences known, 8 have mutations in the N-terminal domain of gK, suggesting that this domain, which is likely to be an ectodomain, is important for the function of the protein. The other two mutants, syn30 and syn103, have mutations near the C terminus of gK.

The oscillatory Belousov–Zhabotinsky reaction with flavones in batch systems using aqueous–DMF mixed medium

Oscillatory systems of the Belousov–Zhabotinsky type with flavones as substrates are described for the first time. Since quercetin and morin are water insoluble, a mixed medium containing DMF and water was used with one of the three catalysts Ce(III), ferroin, or Mn(II). The oscillatory behaviour of a water-soluble substrate (gallic acid) was studied in nine different aqueous–organic mixed media as well as in pure aqueous medium in the bromate–Ce(III) system. The results obtained from a catalyzed system with quercetin or morin as the substrate in an aqueous–organic mixed medium are in agreement with the accepted (FKN) mechanism for an aqueous system.

In vitro characterization of the HSV-1 UL53 gene product

The UL53 gene is the locus altered in many syncytial mutants of herpes simplex virus type 1 (HSV-1). However, the protein encoded by this gene has not been characterized. In this study, the UL53 protein was produced by in vitro translation of in vitro-transcribed UL53 RNA. Post-translational processing of the protein was studied by translation in the presence of pancreatic microsomal membranes. These microsomes carry out the processing steps that normally occur in the rough endoplasmic reticulum. The unprocessed protein had an apparent molecular weight of 27K, whereas the microsomally processed form had an apparent molecular weight of 36K. Two types of post-translational modification were detected: Addition of N-linked oligosaccharides and cleavage of an N-terminal signal sequence. N-linked glycosylation occurred in the first 112 residues of the protein, consistent with the presence of N-linked glycosylation signals at residues 48 and 58. Signal sequence cleavage occurred after residue 30. A membrane-binding, possibly transmembrane, domain was found between residues 113 and 170, probably consisting of the hydrophobic sequence 125-139. These results establish that the N-terminal domain of the UL53 protein, which is the site of those syncytial mutations that have been sequenced, is on the interior side of the microsomal membranes, which is topologically equivalent to the lumen of the rough endoplasmic reticulum and to the extracellular side of the plasma membrane. Additional hydrophobic, possibly transmembrane, domains exist nearer the C-terminus of the protein. It also was found that the in vitro-translated UL53 protein aggregated when heated, even in the presence of SDS. This property was mapped to the C-terminal one-third of the protein.

Complex behaviour of the repressible operon

The repressor-mediated repression process in bacteria is modelled using a gene-enzyme-endproduct control unit. A combined analytical-numerical study shows that the system, though stable normally, becomes unstable for super-repressing strains even at low values of the cooperativity of repression, provided demand for the endproduct saturates at large endproduct concentrations. In addition the system also shows bistability, i.e., the co-existence of a stable steady-state and a stable limit cycle. The tryptophan operon is used as a model system and the results are discussed in the light of differential regulation of gene expression in lower organisms, especially in mutant strains.

On the dynamics of controlled metabolic network and cellular behaviour

The existence of elaborate control mechanisms for the various biochemical processes inside and within living cells is responsible for the coherent behaviour observed in its spatio-temporal organisation. Stability and sensitivity are both necessary properties of living systems and these are achieved through negative and positive feedback loops as in other control systems. We have studied a three-step reaction scheme involving a negative and a positive feedback loop in the form of end-product inhibition and allosteric activation. The variety of behaviour exhibited by this system, under different conditions, includes steady state, simple limit cycle oscillations, complex oscillations and period bifurcations leading to random oscillations or chaos. The system also shows the existence of two distinct chaotic regimes under the variation of a single parameter. These results, in comparison with single biochemical control loops, show that new behaviours can be exhibited in a more complex network which are not seen in the single control loops. The results are discussed in the light of a diverse variety of cellular functions in normal and altered cells indicating the role of controlled metabolic network as the underlying basis for cellular behaviour.

Vibrational frequencies of deuterated ethylenes: Green's function method

The frequencies of the partly deuterated ethylenes were predicted by the method of Green's function analysis. These values are compared with those obtained by the average rule and complete isotope rule. It is shown that the Green's function analysis gives a better insight into the isotopic rule from the molecular dynamic point of view.