The role of negative superhelicity and length of homology in the formation of paranemic joints promoted by RecA protein

Escherichia coli RecA protein pairs homologous DNA molecules to form paranemic joints when there is an absence of a free end in the region of homologous contact. Paranemic joints are a key intermediate in homologous recombination and are important in understanding the mechanism for a search of homology. The efficiency of paranemic joint formation depended on the length of homology and the topological forms of the duplex DNA. The presence of negative superhelicity increased the pairing efficiency and reduced the minimal length of homology required for paranemic joint formation. Negative superhelicity stimulated joint formation by favoring the initial unwinding of duplex DNA that occurred during the homology search and was not essential in the maintenance of the paired structure. Regardless of length of homology, formation of paranemic joints using circular duplex DNA required the presence of more than six negative supercoils. Above six negative turns, an increasing degree of negative superhelicity resulted in a linear increase in the pairing efficiency. These results support a model of two distinct kinds of DNA unwinding occurring in paranemic joint formation: an initial unwinding caused by heterologous contacts during synapsis and a later one during pairing of the homologous molecules.     

Amide modes of the alpha-helix: Raman spectroscopy of filamentous virus fd containing peptide 13C and 2H labels in coat protein subunits

The filamentous virus fd consists of a single-stranded DNA genome sheathed by 2700 copies of a 50-residue alpha-helical subunit (protein pVIII) and serves as a model assembly of alpha-helices. To advance vibrational assignments for the alpha-helix, we have investigated Raman spectra of fd virions containing 13C and 2H (deuterium) labels at various main-chain sites of the pVIII subunits. 13C was introduced at specific peptide carbonyls, while deuterium was introduced at selected alpha-carbon (Calpha) and amide nitrogen positions. Interpretation of the Raman spectra reveals a previously unrecognized alpha-helix band in the spectral interval 730-745 cm-1, tentatively assigned to a carbonyl in-plane bending mode (amide IV). Experimental evidence has also been obtained for a distinctive alpha-helix marker near 1345 cm-1, assigned to a coupled Calpha-H bending and Calpha-C stretching mode. The fd virions containing 13C-labeled carbonyls exhibit unexpectedly complex amide I profiles, consisting of multiple band components. Amide I splitting resulting from 13C substitution of carbonyls is attributed to decoupling of transition-dipole interactions normally occurring in the extended pVIII helix. The present study identifies novel conformation-dependent Raman bands in a native alpha-helix assembly, confirms amide I and amide III assignments proposed previously for filamentous viruses, and facilitates new Raman assignments for the packaged ssDNA. The alpha-helix markers identified here should also be useful in conformation analyses of other proteins by Raman spectroscopy.     

Phyto-oestrogens: where are we now?

Phyto-oestrogens have emerged from their esoteric role in animal husbandry following the hypothesis that the human Western diet is relatively deficient in these substances compared with societies where large amounts of plant foods and legumes are eaten. Evidence is beginning to accrue that they may begin to offer protection against a wide range of human conditions, including breast, bowel, prostate and other cancers, cardiovascular disease, brain function, alcohol abuse, osteoporosis and menopausal symptoms. Of the two main classes of these weak oestrogens, the isoflavones are under intensive investigation due to their high levels in soyabean. Like the 'anti-oestrogen' Tamoxifen, these seem to have oestrogenic effects in human subjects in the cardiovascular system and bone. Although previously only available from food, isoflavones are now being marketed in health-food supplements or drinks, and tablets may soon be available over the counter as 'natural' hormone-replacement therapy. In cancer, anti-oestrogenic effects are thought to be important, although genistein especially has been shown to induce wide-ranging anti-cancer effects in cell lines independent of any hormone-related influence. There are few indications of harmful effects at present, although possible proliferative effects have been reported. In infants, the effects of high levels in soya milk formulas are uncertain. The second group, lignans, have been less investigated despite their known antioestrogenic effects and more widespread occurrence in foods. Investigation of the possible benefits of phyto-oestrogens is hampered by lack of analytical standards and, hence, inadequate methods for the measurement of low levels in most foods. This problem may prove to be a major dilemma for regulatory authorities, clinicians and others wishing to advise the general public on whether these compounds really do have the health benefits attributed to them.     

Needle embolus causing cardiac puncture and chronic constrictive pericarditis

We present a case in which a needle broke off during intravenous injection and embolized to the right heart. After cardiac perforation, the needle entered the pericardial space and ultimately caused chronic constrictive pericarditis, which presented as congestive heart failure. Pericardectomy and removal of the foreign body via a median sternotomy were successful. Early surgical removal of contaminated intrapericardial foreign bodies remains a safe and effective approach to preventing such complications.     

Model for cone directionality reflectometric measurements based on scattering

Reflectometric measurements provide an objective assessment of the directionality of the photoreceptors in the human retina. Measurements are obtained by imaging the distribution at the pupil plane of light reflected off the human fundus in a bleached condition. We propose that scattering as well as waveguides must be included in a model of the intensity distribution at the pupil plane. For scattering, the cone-photoreceptor array is treated as a random rough surface, characterized by the correlation length T (related to the distance between scatterers, i.e., mean cone spacing) and the roughness standard deviation sigma (assuming random length variations of the cone outer-segment lengths that produce random phase differences). For realistic values of T and sigma we can use the Kirchhoff approximation for computing the scattering distribution. The scattered component of the distribution can be fitted to a Gaussian function whose width depends only on T and lambda. Actual measurements vary with experimental conditions (exposure time, retinal eccentricity, and lambda) in a manner consistent with the scattering model. However, photoreceptor directionality must be included in the model to explain the actual location of the peak of the intensity distribution in the pupil plane and the total angular spread of light.     

Course of psychiatric and substance abuse syndromes co-occurring with bipolar disorder after a first psychiatric hospitalization

BACKGROUND: Patients with bipolar disorder frequently meet criteria for other psychiatric and substance abuse diagnoses. To clarify relationships among these disorders, the authors examined the course of syndromes co-occurring with bipolar disorder for 12 months after a first hospitalization. METHOD: Seventy-seven patients were recruited from consecutive inpatient admissions who met DSM-III-R criteria for bipolar disorder, manic or mixed with psychosis. The 12-month syndromal course of co-occurring DSM-III-R alcohol and drug abuse disorders, posttraumatic stress disorder (PTSD), obsessive-compulsive disorder (OCD), and other anxiety disorders were longitudinally recorded. RESULTS: The rates of all syndromes, except other anxiety disorders, were elevated. OCD demonstrated an interval course that frequently mirrored the course of the bipolar disorder. The courses of PTSD and substance abuse syndromes were separate from that of the bipolar disorder in many of those with both syndromes. Alcohol and drug abuse syndromes were strongly correlated. CONCLUSION: The obsessive-compulsive syndrome may represent an alternative expression of bipolar disorder in some patients. In contrast, PTSD appears to represent a truly separate disorder, which is possibly more prevalent in bipolar patients due to a shared risk factor. Substance abuse does not appear to simply result from attempts at self-medication or from the impulsivity of mania. These results suggest that future studies examining the course of syndromes co-occurring with bipolar disorder are warranted.