The eclipse period of Escherichia coli

The minimal time between successive initiations on the same origin (the eclipse) in Escherichia coli was determined to be approximately 25-30 min. An inverse relationship was found between the length of the eclipse and the amount of Dam methyltransferase in the cell, indicating that the eclipse corresponds to the period of origin hemimethylation. The SeqA protein was absolutely required for the eclipse, and DnaA titration studies suggested that the SeqA protein prevented the binding of multiple DnaA molecules on oriC (initial complex formation). No correlation between the amount of SeqA and eclipse length was revealed, but increased SeqA levels affected chromosome partitioning and/or cell division. This was corroborated further by an aberrant nucleoid distribution in SeqA-deficient cells. We suggest that the SeqA protein's role in maintaining the eclipse is tied to a function in chromosome organization.     

A polyhedrosis virus forming polyhedra in midgut-cell nucleus of silkworm, Bombyx mori. II. Chemical nature of the virion

A number of tumorlike lesions of the ctenidia and mantle of the freshwater bivalve Dreissena polymorpha are described. The lesions are not considered to be neoplasms and are similarly not attributable to any of the known parasites of Dreissena. No visible signs of external injury to the affected organs could be detected and it is considered that the granulomas are the result of the hemocyte response of the animal to traumatic irritation or to bacterial infection. The bacteria may be of primary or merely of secondary importance. In the extreme cases examined the granulomas comprised internally a mass of epithelioid cells and granulocytes, surrounded by a proliferation of fibroblasts. Intense inflammatory hyperplasia characterises the surrounding tissues which results, in extreme cases, in distortion of the ctenidial filaments and disturbance to the ciliary feeding currents.Such structures are rarely reported upon in molluscs and throw light on the processes involved in the response to injury in these animals.     

Structural requirement of sterol nucleus for the silkworm growth and development

Several cholesterol analogs structurally modified in nuclear substitutions were tested for sustaining the growth of the silkworm $\text{Bombyx mori}$. 5α-Cholest-7-en-3β-ol, 5,7-cholestadien-3β-ol and cholesteryl acetate can replace cholesterol as sterol source for $\text{B. mori.}$ Considerably good growth was also obained with 5α-cholest-14-en-3β-ol and 5α-cholesta-6,8(14)-dien-3β-ol. Other sterols tested were either partially effective or ineffective as nutrients.     

Studies on the polyhedrosis virus forming polyhedra in the midgut-cell nucleus of the silkworm,Bombyx mori: I. Purification procedure and form of the virion

A procedure for the isolation and purification of a new polyhedrosis virus that forms polyhedra in the midgut-cell nucleus is described. The method is a modification of that used by Hayashi and Bird (1970) for the isolation of free cytoplasmic-polyhedrosis virus (CPV). The purified virions were spherical in shape with several projections that measured 62 nm in diameter. The sedimentation coefficient of this virion was 430 S. These features are very similar to those of CPV. No significant difference was observed between this virus and CPV in the sedimentation profiles of preparations. Electron microscope observations indicated that the purified virus preparations contained many more empty particles than those of CPV.From these results, it is concluded that this virus is quite similar to CPV.     

Biochemical and biophysical properties of flacherie virus of the silkworm

Flacherie virus of the silkworm (FVS) was extracted from diseased silkworms, both larvae and pupae, and purified by 15 to 30% sucrose density gradient centrifugation. FVS III and FVS IV, in addition to the FVS I and FVS II described in the previous paper (Himeno et al., 1974), were found. The FVS I, FVS III, and FVS IV showed the same mobility in 2.4% polyacrylamide gel electrophoresis and could not be distinguished from each other in the gel. However, the purified FVS II was separated into two bands, FVS IIa and FVS IIb, in 2.4% gel. FVS III was a spherical particle with a diameter of 28 ± 1 nm and showed a sedimentation coefficient of about 90 S. FVS III was easily decomposed into FVS IV which sedimented at about 30 S in sucrose gradient centrifugation. FVS I and FVS II each contained a single molecule of RNA which showed the same molecular weight. FVS I consisted of three polypeptides with molecular weights of 67,000, 50,000, and 33,000. FVS II consisted of 10 polypeptides; among them 2 polypeptides with molecular weights of 50,000 and 33,000 were also found. Labeling experiments with [³²P]orthophosphate revealed that FVS II was found at an early stage of infection and FVS I at a late stage. FVS II was also isolated at an early stage from silkworms infected with FVS II, and FVS I was found at a late stage in these silkworms. The correlation among FVS I, FVS II, FVS III, and FVS IV was discussed and it was suggested that they might be closely related to one another and that few particles in them were immature. It is possible that FVS II changes to FVS I via FVS III by cleavage of large polypeptides.     

EMBO workshop report. An eclipse over the cell nucleus functional organization of the cell nucleus Prague, August 9-12, 1999

The EMBO workshop 'Functional Organization of the Cell Nucleus' held in Prague at the Hotel of the Postgraduate School of Medicine was attended by 110 participants (49 invited speakers and 61 selected participants) from 22 countries. Such a full range of topics devoted to the cell biology of the nucleus has not been discussed previously in such an intimate meeting in Europe. The workshop not only offered an opportunity for junior scientists to benefit from having an international meeting within Europe and a chance to discuss their work with internationally recognized experts, but it also offered a unique opportunity for interactions among the more established investigators. The fruits of a number of presentations are gathered together in a Special Issue of the Journal of Structural Biology which appeared in spring 2000. Last but not least, it is worth mentioning that while stepping through a packed scientific program, the participants did find the time to observe the solar eclipse just before the lunch break of August 11.