A small (2.4 Mb) Bacillus cereus chromosome corresponds to a conserved region of a larger (5.3 Mb) Bacillus cereus chromosome

We have determined the sizes of the chromosomes of six Bacillus cereus strains (range 2.4–4.3 Mb) and constructed a physical map of the smallest B. cereus chromosome (2.4 Mb). This map was compared to those of the chromosomes of four B. cereus strains and one B. thuringiensis strain previously determined to be 5.4-6.3 Mb. Of more than 50 probes, 30 were localized to the same half of the larger B. cereus and B. thuringiensis chromosomes. All 30 were also present on the small chromosome. Twenty of the probes present on the other half of the larger chromosomes were either present on extrachromosomal DNA, or absent from the B. cereus strain carrying the small chromosome. We propose that the genome of B. cereus and B. thuringiensis has one constant part and another less stable part which is more easily mobilized into other genetic elements. This part of the genome is localized to one region of the chromosome and may be subject to deletions or more frequent relocations between the chromosome and episomal elements of varying sizes up to the order of megabases.     

‘De novo’ centrioles originate at sites associated with annulate lamellae in sea-urchin eggs

Hypertonic stress stimulates the formation of new centrioles in sea-urchin eggs. Those centrioles which appear away from the nuclear surface originate exclusiveJy at sites associated with annulate lamellae. Although apparent when nascent centrioles become visible, the annulate lamellar association is gradually lost as nascent forms mature into centrioles.     

Substrate binding to solubilized cytochrome P-450 from rabbits at different temperatures.

The binding affinities of selected type I- and type II-substrates to partially purified cytochrome p-450 from rabbit liver microsomes were studied and found to differ from those of rats. The temperature dependence of the apparent binding constants qualitatively exhibited the same characteristics compared with that of rats. For type I-substrates endothermic and for type II-substrates exothermic reaction characteristics were observed. Taking into account the partition coefficients of the substrates so far investigated it is obvious that type I substrates with increasing hydrophobicity are bound more strongly while type II-substrates show a more complicated behvaiour. This may due to the fact that other types of binding are included besides the hydrophobic interactions.     

Interaction of a folded chromosome-associated protein with single-stranded DNA-binding protein of Escherichia coli, identified by affinity chromatography

A single-stranded DNA-binding protein (SSB) affinity column was prepared by optimizing the coupling of Escherichia coli single-stranded DNA-binding protein to Affi-Gel 10. The bound SSB retained its ability to specifically bind single-stranded DNA. When nuclease-treated cell extracts were incubated with the SSB beads overnight at 4 degrees C, a major protein of Mr = 25,000 was bound. At shorter incubation times, two additional proteins of Mr = 32,000 and 36,000 were also detected. In the absence of nuclease treatment, eight additional proteins ranging from Mr = 14,000 to 160,000 also bound to the affinity column. The major Mr = 25,000 protein has been shown to be a folded chromosome-associated protein. Its binding to SSB is strongly enhanced by the addition of DNA polymerase III or DNA polymerase III holoenzyme.     

Structural Requirements for a Primitive Adaptor Molecule

Abstract

Adaptor properties of linear hairpin helices have been examined. The analysis suggests that neither right nor left handed hairpin helices can simultaneously read a comma free messenger and align aminoacyl residues for peptide condensation. Comparison of these studies with the model of the present day peptidyl transfer intermediate suggests that the “L” shaped folding of the present day tRNAs may be a prerequisite for adaptor function. Therefore, the three-dimensional organization of the ancestral adaptor molecule must have had structural features similar to its present day counterpart.     

Neuropharmacological Analysis of Mechanisms Controlling Larval Behaviour in the Sea Urchin; 1. Effects of carbamylcholine and acetylcholine

The effect of carbamylcholine (carbachol) on the muscular, intestinal, and ciliar activities of the sea urchin pluteus larva (Psammechinus miliaris) show a complicated relation between the concentrations used, the length of exposure, and the physiological responses. Two main patterns of stimulated activity emerged upon carbachol treatment. In pattern I there is a reciprocal “antagonism” between swallowing and celomic movements, i.e. stimulation of one type of movement is attended by a decrease of the other type and even its complete paralysis. Paralysis of the celomic movements is attended by intestinal paralysis. In pattern II marked swallowing and celomic activity coexist. The fluctuations in these activities are strong, their maxima as well as their minima coincide, and intestinal cycling occurs. In pattern I low concentrations favour the celomic activity and counteract swallowing. At higher concentrations the initial effects are qualitatively similar but more intense and of short duration. They are quickly followed by the opposite effects (intense swallowing and celomic paralysis) together with intestinal paralysis. The effects are to a great extent quickly reversible after transfer of the larva to sea water. During prolonged or repeated exposure to the agent the system “adapts”, i.e. a pattern II activity may appear. If the concentration is not too high, this may be preceded or admixed by a renewed pattern I activity. The responses described suggest that two main control systems are involved in the regulation of the larval activities. The effects of acetylcholine are similar to those of carbachol but not identical. The question if the control mechanisms are related to regionally separated structures is discussed in a preliminary way.