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Biomedical subjects

K Zahn

Publications and source records attributed to K Zahn.

15 recordsLinked to original sources
PubMed1992

[Do the obstetrically relevant bony pelvic measurements change? A retrospective analysis of computed tomographic pelvic x-rays].

The important dimensions of pelvimetry were evaluated from 467 CT studies of the pelvis by trigonometric deduction. The age of the women was between 18 and 88 years. In addition to the diameters, which are routinely used for pelvimetry, transverse and sagittal diameters, pelvic angles and areas of pelvic planes were calculated. On condition that the pelvic dimensions do not depend on age the parameters can be regarded as representative of sexual maturity. 5 parameters showed highly significant and 7 parameters showed significant differences between the age-classes 1901-1920 and 1950-1971. An increase of pelvic dimensions (1950-1971) was found at the planes of the pelvic inlet and outlet in contrast to the dimensions of the pelvic center. The results confirm the importance of the bispinous diameter for pelvimetry as well as the demand for a revision of the standard values of the first half of the century.

Adolescent↗
PubMed1989

DNA looping induced by bacteriophage lambda O protein: implications for formation of higher order structures at the lambda origin of replication.

A plasmid has been constructed, pOri2, which contains two lambda replication origin sequences separated by 1068 bp; both lambda sequences having the same orientation. When lambda initiation protein O is reacted with linearized pOri2 and examined by electron microscopy it is found to contain a looped area in which two parts of the plasmid are bound together by the O protein complex. Length measurements show that the O protein binds at the expected positions of the lambda origin sequences and that the looped area represents the DNA segment between the two O protein binding domains. Similar looping occurs in reactions with supercoiled pOri2 or if an amino-terminal fragment of O protein is used. When looped molecules are reacted with psoralen, crosslinked by irradiation with uv light, and then denatured, it is found that the looped area is more thermostable than the rest of the molecule. This indicates that the DNA within the looped segment is torsionally constrained while that outside the loop is free to rotate and suggests that simultaneous binding of O to two origins fixes the linkage number of the intervening DNA. The double origin binding ability of O may be diagnostic of the details of the reaction of O with a single origin sequence. A model is presented that rests on the assumption that O can produce microscopic looping between O protein binding sites within a single ori sequence.

Bacteriophage lambda↗
PubMed1988

Initiation protein induced helix destabilization at the lambda origin: a prepriming step in DNA replication.

The interaction of the lambda phage initiator protein, O, with the lambda origin sequence, ori, has been investigated. Binding of O, or its amino-terminal fragment, causes a major structural change within a 60 bp AT-rich region just to the right of the O-binding site. ATP or other molecular energy sources are not required. The modification, as assayed by nuclease sensitivity, is reduced when certain ori mutant sequences, which bind O but fail to replicate, are substituted for the wild-type sequence. The modification of DNA structure caused by the interaction of O is absolutely dependent on the presence of superhelical tension at the lambda origin sequence, and has several properties consistent with a strand separation reaction. We propose that this modification is a fundamental prepriming event that is the first stage in initiation of bidirectional replication in lambda after O binding.

Bacteriophage lambda↗
PubMed1987

Direct evidence for DNA bending at the lambda replication origin.

Replication initiation in bacteriophage lambda appears to require wrapping of origin DNA on an approximately 50 angstrom radius in or around the complex with the initiator protein O. Since short lengths of DNA are not that flexible, it may be that runs of coherently spaced deoxyadenylate residues constitute bend sites in the ori sequence that facilitate the process. Earlier data showed that ori DNA has electrophoretic anomalies characteristic of bend sites and that these are augmented by initiator protein binding. Here origin bending is examined by direct measurement of the ability of polymerized ori sequences to form small circles. The smallest circles observed (84 residues) are compatible with the required radius of curvature. Bend sites within the O protein binding sites, bend sites in the spacers between them, plus the inherent flexibility of non-bent DNA in the origin may all contribute to origin bending. The data also show that a bend site is required for O protein binding to DNA.

Bacteriophage lambda↗
PubMed1986

Characterization of the DNA binding domain of bacteriophage lambda O protein.

The lambda O and P gene products are required for the initiation of lambda DNA replication. In order to study the biochemistry of this process, we have constructed plasmids that carry the lambda O gene, P gene, and half of the O gene coding for the amino-terminal half of the O protein. Each is under the control of the inducible lambda promoter, PL. We have purified these three proteins from induced cells carrying the plasmids. Our results show that the amino-terminal portion of the O protein binds to the lambda origin of replication in a manner similar to the intact lambda O protein, demonstrating that the amino-terminal portion of O protein contains the DNA binding domain. Using chromatographic procedures, we have isolated a complex of lambda O and P proteins with lambda dv DNA. The amino-terminal portion of the O protein does not complex with P protein under the same conditions. This suggests that the specificity of the lambda O protein for P protein resides in the carboxyl-terminal half of the lambda O protein. Our results also show that, while the intact O protein is active in in vitro replication of lambda dv plasmid DNA, the amino-terminal portion of the O protein is inactive and is a competitive inhibitor of the lambda O protein in this reaction. These results confirm previous genetic observations that were interpreted as indicating a bifunctional structure for the lambda O protein with the amino-terminal domain recognizing the lambda origin of replication and the carboxyl-terminal domain interacting with the lambda P protein.

Bacterial Proteins↗
PubMed1985

Binding and bending of the lambda replication origin by the phage O protein.

We have characterized the binding of lambda phage replication initiation protein O to the phage origin of replication. The minimal DNA segment required for O binding is the single iteron, a 19-bp sequence of hyphenated dyad symmetry that is repeated with variations four times in the origin. The isolated amino terminus of O protein is also sufficient to bind DNA. Electrophoretic studies show that the amino terminus of O protein induces bending of a single iteron. The DNA-protein interaction was characterized by ethylation interference, dimethyl sulfate protection and neocarzinostatin footprinting. Points of DNA-protein contact are largely concentrated in two areas symmetrically disposed with respect to the dyad symmetry of the iteron. This suggests the protein interacts as a dimer with half sites in the DNA. However, a few non-symmetrical contacts are found, indicating that O protein may distort the helix. This may correlate with the bending effects demonstrated electrophoretically. Cylindrical DNA projections were used to model O protein binding to the lambda origin and compare it with the lambda repressor-operator interaction. Whereas bound repressor nearly encircles the DNA in the major groove, O protein leaves the major groove on the opposite side exposed.

Alkylation↗
PubMed1978

The synthesis of ninety proteins including actin throughout the HeLa cell cycle.

Abundant cytoplasmic proteins pulse-labeled with [35S]methionine at specific times throughout the HeLa cell cycle were analyzed with two-dimensional gel electrophoresis. More than 300 proteins could be resolved in this way. The frequency of appearance of label in the most abundant 90 proteins, ranging from 4% to less than 0.1% of the total methionine incorporated, was determined at six time points in the cell cycle. 84 of these proteins were made as a similar proportion of the total at all times during the cell cycle. A nonmuscle actin protein (spot 1) identified by molecular weight and isoelectric point represented 2-4% of the total methionine incorporated at all the time points. Only six proteins were found which varied by greater than fourfold during cell division, four appearing to represent a greater proportion of the total synthesis during the period at or immediately surrounding M (spots 31b, 44, 53, and 70d). Two appear to represent a smaller percentage of total synthesis during the early (spot 78) or the total (spot 74) G2 period.

Actins↗
PubMedDate not supplied

Sequence-induced DNA curvature at the bacteriophage lambda origin of replication.

DNA replication in bacteriophage lambda begins at a unique origin between residues 39,000 and 39,200 of the lambda genome. This segment of DNA serves a dual function since it also lies within the coding sequence of the lambda replication initiator protein O which binds origin DNA. The lambda origin sequence contains four 19-base-pair (bp) segments (iterons) which have dyad symmetry, followed by a 40-bp A + T-rich zone of highly asymmetrical base composition. It was noted earlier that lambda origin DNA exhibits an anomalous electrophoretic mobility on gels; that is, the length of DNA as determined by DNA sequencing is approximately 20% less than is predicted from electrophoretic mobility. Recent studies of kinetoplast minicircle DNA (K-DNA) from the protozoan Leishmania tarentolae have led to the proposal that sequence-induced DNA curvature could account for such electrophoretic anomalies by alteration of the shape of the DNA molecule. We now present evidence that the lambda origin contains a static curve.

Bacteriophage lambda↗
PubMedDate not supplied

[Changes in pelvic anatomy in 8 decades--computerized tomography study of obstetrically relevant pelvic measurements].

An increasing proportion of obstetric operative procedures due to cephalopelvic disproportion gave raise to the question, whether there has been a change in pelvic anatomy during the past decades. In a retrospective evaluation of 467 computerized pelvic tomograms of patients aged between 18 and 88 years relevant parameters of pelvic proportion were determined. As these parameters are not subject to age-conditioned changes, the values may be viewed as representative for the time of patients' birth or fertility period respectively. Changes in pelvic anatomy turned out to be complex: The transverse elliptic shape of pelvic inlet changed into sagittal elliptic form, the pelvic midplane is contracted progressively, sacral concavity is reduced. Obviously, this obstetrically adverse development is influenced by the fact, that unfavourable pelvic conformation can be transmitted more intensively by the generous indication for cesarean section. This development is contrasted by the circumstance of fetal acceleration. Therefore, an increase in cephalopelvic disproportion has to be expected. For the sake of a safe obstetrical management in these situations the generous use of ante partum pelvimetric diagnosis seems to be advisable.

Adolescent↗