Studies of the interaction of RecA protein with DNA

Ethidium fluorescence assays were adapted for the rapid and sensitive detection of precA; in addition, fluorescence measurements on binding precA to linear, OC and CCC PM2 DNAs have enabled the stoichiometry of precA binding as well as the precA-induced unwinding angle of DNA to be determined. The stoichiometry of binding was independently confirmed by sedimentation analysis to be one precA molecule per 3 bp. The unwinding angle was also independently confirmed by measurements of fluorescence changes induced by the binding of precA to CCC DNA which was relaxed by topoisomerase to give a precA-induced unwinding angle of 51 degrees. Electron microscopy of OC DNA molecules which bound nonsaturating amounts of precA revealed that the length increase in DNA due to precA was approximately 55%. Finally, examination of negatively stained precA complexes with a variety of linear DNAs showed that the minor groove is the primary site of interaction for this protein.     

Some observations of Octopus joubini reared in an inland aquarium

Octopus joubini Robson were hatched and reared in a closed circulating sea-water system. Mortality was greatest during the period of hatching. The longest surviving octopus lived for 128 days—it had increased its weight × 5, from 0·04–0·19 g, mantle length × 3, from 3–9 mm, head width × 2, from 3–5 mm. Observations of (1) general behaviour, (2) feeding behaviour, (3) social behaviour of the newly hatched octopuses (0–3 days) and the three longest surviving octopuses (93–119 days) are described. In particular it was observed that the older octopuses would readily grasp and eat small live crabs when these were made to touch the suckers or arms. On no occasion did the attacks appear to be visually elicited. This result is discussed with reference to the memory and learning experiments using O. vulgaris. Possible reasons for the limited survival are also discussed.     

Increased free-cystine content of fibroblasts cultured from patients with cystinosis

The presence of a significantly increased content of free-cystine in skin fibroblasts from both homozygotes and heterozygotes for cystinosis emphasizes the central role of cystine in this disease, even though the primary defect responsible for cystine accumulation is yet to be determined. The studies described in this communication provide evidence that cystine is compartmentalized in a subcellular location in cystinotic cells. In fact, the very growth of cystinotic fibroblasts in the presence more than 100 times the usual content of free-cystine is evidence that the accumulated cystine is not freely dispersed throughout the cell, since would otherwise inhibit many enzymes requiring free sulfhydryl groups for activity (Patrick, 1965). We have no evidence as to whether the cystine is located in a known subcellular organelle or in a previously unrecognized location. Skin fibroblasts may provide a convenient tool to pursue these questions.     

Circular dichroism measurements of benzyl L-aspartate–nitrobenzyl L-aspartate copolymers and their use in detecting and characterizing preferred polymer conformations

We have examined the nature of the circular dichroism band at 330 mμ for a series of copolymers of β-p-nitrobenzyl L -aspartate with β-benzyl L -aspartate. The circular dichroism band arises from an electronic transition in the nitroaromatic group. In order to interpret the effect quantitatively, we employed a simplified statistical treatment and curve fitting for six copolymers. Both approaches gave consistent results, which indicates that the dichroism comes from pairwise interactions between two nitrobenzyl groups. We constructed a molecular model that meets the constraints and requirements of the analyses developed in this paper. In this model, it is proposed that the main chain forms a right-handed α-helix and that nitrobenzyl groups separated by four residues interact with each other.     

Heparin-binding growth factors and their receptors

Heparin-binding growth factors modulate diverse biological activities including cellular proliferation, cellular differentiation, morphogenesis, and angiogenesis. Biochemical characterization for two members of the heparin-binding growth factor family, acidic and basic fibroblast growth factors, is extensive, while characterization of the remaining five members is forthcoming. Cell surface receptors have been identified for acidic and basic fibroblast growth factors, but little is known concerning their sites of action in vivo or the mechanisms involved in transducing the energy of growth factor binding to a biological response. An understanding of the biological basis for the diversity of the heparin binding growth factor family and the in vivo actions of these factors will prove a major challenge to future research efforts.