Construction of a microphage variant of filamentous bacteriophage.

The intergenic region in the genome of the Ff class of filamentous phage (comprising strains fl, fd and M13) genome constitutes 8% of the viral genome, and has essential functions in DNA replication and phage morphogenesis. The functional domains of this region may be inserted into separate sites of a plasmid to function independently. Here, we demonstrate the construction of a plasmid containing, sequentially, the origin of (+)-strand synthesis, the packaging signal and a terminator of (+)-strand synthesis. When host cells harboring this plasmid (pLS7) are infected with helper phage they produce a microphage particle containing all the structural elements of the mature, native phage. The microphage is 65 A in diameter and about 500 A long. It contains a 221-base single-stranded circle of DNA coated by about 95 copies of the major coat protein (gene 8 protein).

Power to the portables.

Portable computing devices generally are classified into four categories: laptop, palmtop, notebook, and pen-based computers. If a portable unit weighs over eight pounds, call it a laptop. If a stylus is used to input data, call it pen-based or a pen computer. Palmtops frequently are electronic organizers or resources: Sharp's Wizard line stores appointments and addresses; Franklin's Med-Spell contains Stedman's medical dictionary. Notebooks often incorporate a QWERT keyboard, and sometimes include a pointing device. NEC's notebooks in 1988 were the first sub-laptop computers. According to a 1992 report from Market Intelligence Research Corp., Mountain View, Calif., 4.6 million sub-laptops were sold in 1991 for $2.6 billion. By 1998 the market may reach $25 billion. The report predicts that one sub-category of pen computers, which are designed to be held in one hand while information is input with a pen-like stylus, will prove most useful to the health-care industry. Pen tablets, as opposed to pen clipboards, use faster, more expensive processors, store more data, and "are expected to allow [caregivers] to carry full patient charting with them ... and allow information to be recorded directly to patient files." Sub-laptops are on-line in many healthcare facilities: Greenwich hospital, Stanford University Medical Clinic, Humana Hospital Audubon, Rancho Los Amigos Medical Center, and others.

Structural responsiveness of filamentous bacteriophage Pf1: comparison of virion structure in fibers and solution. The effect of temperature and ionic strength.

X-ray diffraction from fibers and magnetically oriented solutions has been used to study the effect of changes in environment on the helical symmetry and radial structure of the Pf1 virus particle. Detailed analysis of equatorial scattering to a spacing of 8-10 A was used to identify small radial motions of structural elements in the virus particle. R-factor ratios were used to determine the statistical significance of observed changes. Comparison of the structure of virus particles in fibers with those in solution indicated that the helical symmetry of the virions remains unchanged during fiber formation. In most fibers the virions appear to be slightly distorted by the tight packing of virus particles. This distortion results in an apparent increase in the radius of the virus particle of approximately 0.6 A. A change in the radius of the DNA is also observed. Increase in the concentration of solvent molecules during fiber formation results in penetration of the virus interior by some solvent components. NaCl is also able to enter the virus interior. The change in the helical symmetry of the virions at approximately 8 degrees C appears to be the same whether observed by diffraction from fibers or from solutions. Only subtle changes in radial structure are associated with the temperature transition.

Electronmicroscopy and circular dichroism of the dynamics of the formation and dissolution of supramolecular forms of Z-DNA.

Previous electronmicroscopic studies had shown that N-acetylaminofluorene (AFF)-substituted poly(dG-dC)-poly(dG-dC) in the Z conformation, in 10mM Mg++, condensed into periodically banded, branched structures. We now show that similar structures are seen when poly(dG-dC)-poly(dG-dC) is converted to the Z conformation by heating to 60 degrees C in 1mM Mn++ or to 65 degrees in the presence of 0.5mM Mn++. We demonstrate that these banded structures form in solution, i.e. they are not artifacts of the preparative procedures used for electronmicroscopy, by crosslinking the Z conformers in solution with DL-diepoxybutane (DEB), and then restoring the solution to conditions that favor return to the B conformation. Circular dichroism (CD) and immunochemical studies showed that the Z conformation was maintained and the banded supramolecular structures were still seen by electronmicroscopy. Electronmicroscopy and CID were also used to follow the dissolution of the supramolecular structures by controlled scission of the crosslinks with the eventual return to the short double stranded molecules typical of the B conformers. During this process, supercoiled structures, both toroidal and interwound, were observed. The relationship of the toroids to the banded structure is discussed in the context of two possible structures for the condensed polynucleotide. We conclude that DNA, whether in the B or Z conformation, is extremely flexible in the presence of appropriate counter ions, and we present evidence that earlier estimates of their persistence lengths are too high. The inherent tendency to form condensed, highly organized structures is a property of DNA that could play an important role in its "packaging," and in its functions, and might have been critical for the evolution and replication of early life forms.