Biomedical subjects
Publications and source records attributed to B Unger.
After 8 years of comparison to MV, BP reveal no significant difference in early mortality and late survival statistics, yet demonstrated a higher rate of late complications such as endocarditis and perivalvular leak. In conclusion our data indicate that BP are not superior to MV after 8 years of follow-up.
The purpose of this study was to determine the incidence of work-related low back pain (LBP) in physical therapists and to identify common characteristics of therapists who reported work-related LBP. Questionnaires were mailed to a random sample of 500 registered physical therapists. Of the 344 (69%) questionnaires returned, 29 percent reported work-related LBP. The initial onset most frequently occurred between the ages of 21 and 30 years and within the first four years of experience as a physical therapist. Eighty-three percent of the therapists first incurred work-related LBP during treatment of patients, primarily in acute care and rehabilitation facilities. "Lifting with sudden maximal effort" and "bending and twisting" were frequent mechanisms of injury. Further research is necessary to investigate the effect work-related LBP has on productivity and quality of patient care within facilities and to identify preventive measures to decrease the incidence of work-related LBP.
Homologous and heterologous repressor-operator interactions among four different classes of tetracycline resistance determinants have been compared. These are represented by RP1/Tn1721 (class A), R222/Tn10 (class B), pSC101/pBR322 (class C), and RA1 (class D). By the use of the purified repressor proteins of class A (TetRA) and class B (TetRB), operator sequences of all four classes are recognized by both with an identical stoichiometry of four repressor subunits per control sequence, but with different affinities. In vitro transcription has been used to demonstrate regulatory activities of TetRA and TetRB upon all four classes of tet genes. Tetracycline acted as an inducer. A functional relationship among the tet regulatory systems was also shown in vivo by complementation of a class A tetR'-galK fusion mutant with the tetR genes of classes A, B, and C. Repression of tetRA-linked galactokinase was ca. 80% in the presence of tetRA or tetRC, and ca. 50% in the presence of tetRB. Taken together, these results demonstrate heterologous repressor-operator interaction, suggesting close relationships among the four classes of Tcr determinants.
The tetracycline resistance determinant of RA1 was cloned. It consists of at least two genes oriented with opposite polarity, tetA for resistance and tetR for regulation. The transcriptional control sequence was identified and analyzed. It consists of overlapping promotors with divergent orientation and a tandem arrangement of operators. Nucleotide sequencing revealed two open reading frames. One codes for a protein which was identified as a Tet repressor by comparing its primary structure with those of other Tet repressors. The RA1 tetR gene codes for 218 amino acids with a calculated molecular weight of 24.4 kDa. In the primary sequence of the RA1-, pSC101-, Tn10-, and RP1/Tn1721-encoded Tet repressors, 36% of the amino acids are identical. This homology is clustered within the first 150 amino acids, 49% of which are identical among all four proteins. These results are discussed with respect to their structure and function in comparison to other DNA binding proteins.
The nucleotide sequence of the pSC101-encoded tetracycline repressor gene (tetR) was confirmed. The deduced amino acid sequence is compared to that of other repressor proteins. To overproduce the repressor protein, tetR was placed under the control of bacteriophage lambda promoter pL. Tet repressor protein was purified to homogeneity and shown to bind specifically to two tet operators and also to tetracycline (Tc). The inducer function of Tc is demonstrated by the loss of the specific binding between the tet operator DNA and the Tet repressor-Tc complex.
Interaction of the Tn10 encoded TET repressor with the tet operator is studied by thermal denaturation of the specific complexes employing operator containing purified DNA restriction fragments varying in length from 187 bp to 501 bp. Comparison of the melting curves obtained with the free DNA and DNA.repressor complexes revealed a specific stabilisation of the operator containing cooperatively melting segment in multiphasic denaturation curves. Under limiting concentrations of TET repressor the denaturation of the free DNA is observed next to the denaturation of the repressor.DNA complex. Quantitative analysis yields a binding curve with a stoichiometry of four TET repressors per tet operator containing fragment. The denaturation temperature of the complex is almost independent of the ionic strength indicating that the protein component denatures at this temperature. The half life time of the TET repressor.tet operator complex is greater than 100 min under these conditions. The tet operator on the 187 bp fragment is determined to be located between a Xba I and a Sau 3a site by removing base pairs from either end of the fragment and subsequent comparison of the melting curves. It is concluded that the TET repressor recognizes the double stranded rather than a possible cruciform structure of the tet operator. The influence of a regulatory protein on the thermal stability of a genetic control region is discussed with respect to its possible influence on the initiation of transcription.
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The thermal stability of the Tn10 encoded tetracycline resistance (TET) gene control region is investigated by melting studies using purified DNA restriction fragments containing various amounts of flanking sequences. In order to study the thermodynamic properties of this control region under conditions, where enough flanking DNA is present to mimic the situation in the chromosome, the five step melting process of a 1450-bp DNA fragment is analyzed. Because most of the sequence of this DNA is not known, the assignment of the melting transitions to segments of the DNA is done by an experimental method. This employs the preparation of subfragments from the 1450-bp DNA and comparison of their denaturation profiles with the one of the intact sequence. This approach results in the complete assignment of the five denaturation steps. Rather than from the ends, the unwinding starts from the TET gene control region in the middle of the 1450-bp sequence. A clear correlation between the thermodynamic and genetic properties of this DNA is observed. The regulatory sequence forms a small cooperative unit with the lowest stability in the entire fragment. The thermal denaturation of the TET repressor. TET operator complex reveals, that the TET repressor specifically recognizes the double stranded TET operator DNA and stabilizes this structure by 2.4 degrees C. This results is also discussed as an example of the possible action of denaturing or stabilizing proteins on this genetic control region.
The murein and membrane protein compositions of Caulobacter crescentus strains CB13B1a and CB15 have been characterized, and the influence on cell envelope constituents of culture conditions which affect morphogenesis have been studied. Amino acid and sugar analysis of murein sacculi revealed a simple A1gamma murein configuration typical of gram-negative bacteria. The membranes of C. crescentus had low levels of 2-keto-3-deoxyoctonate relative to enteric bacteria, in addition to the absence of lipid A components (Shapiro et al., Science 173:884-892, 1971; Chow and Schmidt, J. Gen. Microbiol, 83:369-373, 1974). Nevertheless, C. crescentus membranes could be fractionated into inner and outer membrane components by sucrose density gradient centrifugation procedures developed for Escherichia coli. The proteins of the outer membrane were distributed between three major (I, II, and III) and two minor (IV and V) protein classes. Class I proteins were greater than or equal to 74,000 daltons and constituted the primary proteins of the outer membrane. Class I proteins were separated into approximately 50 polypeptides by two dimensional gel electrophoresis; the protein composition of thi s class was affected by culture conditions in both CB13B1a and CB15. Class II (47,000 to 39,000 daltons) and III (20,000 to 11,500 daltons) proteins differed in each strain in composition and response to culture conditions.
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