Characterization of some isolates of newly recovered avian sarcoma virus.

We previously reported the isolation of a newly recovered avian sarcoma virus (rASV) from tumors of chickens injected with transformation-defective (td) mutants of the Schmidt-Ruppin strain of Rous sarcoma virus (SR-RSV). In this paper, we present further biological and biochemical characterization of the recovered sarcoma viruses. High titers of rASV's were generally obtained by cocultivation of tumor cells with normal chicken embryo fibroblasts or by homogenization of tumor tissues. Most rASV isolates were similar to SR-RSV, subgroup A (SR-RSV-A), in their growth characteristics and were nondefective in replication. The subgroup specificity of rASV's and the electrophoretic mobilities of their structural proteins were the same as those parental td viruses. The nondefectiveness of rASV's was further substantiated by the size of their genomic RNA, which was indistinguishable from that of SR-RSV-A and substantially larger than that of parental td RNA. Molecular hybridization using complementary DNA specific to the src gene of SR-RSV (cDNAsrc) showed that the RNAs of td mutants used in this study contained extensive deletions within the src gene (7 to 30% hybridization with cDNAsrc); the same probe hybridized up to 90% with RNA from two isolates of rASV. These data indicate that rASV has regained genetic information which had been deleted in the td mutants and strongly suggest that the generation of rASV involves a genetic interaction between td virus and host cell genetic information.     

Chemical and biological consequences of β-decay

Summary Radioactive decay in a labelled molecule leads to specific chemical and biological consequences which are due to local transmutation effects such as recoil, electronic excitation, build-up of charge states and change of chemical identity, as well as to internal radiolytic effects. In the present paper these effects are reviewed emphasizing the relation of the chemical alterations on a molecular level to the biological manifestation. Potential importance of this type of research for biomedical applications is pointed out. In part 1 we review the underlying physical and chemical principles and consequences of -decay of³H,¹⁴C,³²P,³³P,³⁵S and¹²⁵I for gaseous and simple condensed organic systems. Part 2 which will appear in the next issue will include the discussion of biological effects associated with -decay.     

Medial edge epithelium fate traced by cell lineage analysis during epithelial-mesenchymal transformation in vivo.

Vital cell labeling techniques were used to trace the fate of the medial edge epithelial (MEE) cells during palatal fusion in vivo. Mouse palatal tissues were labeled in utero with DiI. The fetuses continued to develop in utero and tissues of the secondary palate were examined at several later stages of palatal ontogeny. The presence and distribution of DiI was correlated with the presence of cell phenotype-specific markers. During the initial stages of palatal fusion the DiI-labeled MEE were present in the midline position. These cells were attached to an intact laminin-containing basement membrane and contained keratin intermediate filaments. At later stages of palatogenesis the DiI-labeled MEE were not separated from the mesenchyme by an intact basement membrane and did not contain keratin. In late fetal development, DiI-labeled cells without an epithelial morphology were present in the mesenchyme. The transition of the DiI-labeled cells from an epithelial phenotype to a mesenchymal phenotype is consistent with a fate of epithelial-mesenchymal transformation rather than programmed cell death.     

Gas dispersion in volume-cycled tube flow. I. Theory.

A mathematical theory is derived for the dispersion of a contaminant bolus introduced into a fully developed volume-cycled oscillatory pipe flow. The convection-diffusion equation is solved for a tracer gas bolus by expressing the local concentration field as a series expansion of derivatives of the area-averaged concentration. The local, as well as the area-averaged, concentration is determined for a uniform initial slug or Gaussian bolus. The effect of various flow parameters such as Womersley parameter, Schmidt number, and tidal volume is investigated. The overall dispersion is characterized by a time-averaged effective diffusion coefficient, which for long duration coincides with previous dispersion theories based on a constant linear axial concentration profile. The effective diffusion coefficient can be determined from the local time history of concentration, independent of the spatial location or the initial tracer bolus. Furthermore the local peaks of the concentration-time curve follow a decaying curve dictated by the time-averaged effective diffusion coefficient. Thus the theory is directly applicable for dispersion measurements in oscillatory tube flows, a basis for the pulmonary airways application, as shown by Gaver et al. (J. Appl. Physiol. 72: 321-331, 1992).     

Mutations affecting the regulation of γ-aminobutyrate utilization inEscherichia coli K-12

Four genes,gabCPDT, are involved in the utilization of γ-aminobutyrate (GABA) byEscherichia coli K-12. Thegab gene cluster maps nearrecA andsrl, at 57.5 min.gabP, gabD andgabT specify the synthesis of GABA transport carrier, succinic semialdehyde dehydrogenase (SSDH), and glutamate-succinic semialdehyde transaminase (GSST), respectively;gabC controls the synthesis of all three proteins. GABA-nonutilizing mutants carrying deletions insrl extended into thegab cluster have been isolated. The mutants completely lost the capacity for GABA transport, while preserving full activity of GSST and SSDH, suggesting thatgabC is not a promoter-operator locus or a gene coding for an activator protein. A mutation ingabD (M-16) that abolished SSDH activity had the following additional properties: It exerted a bipolar effect on the neighboring genes, greatly reducing the activities of GSST and SSDH; the polar effect ongabP but not ongabT was fully suppressed by the knownrho mutation suA78; at least three classes of GABA-utilizing revertants of M-16 were obtained: (i) revertants with allgab activities restored to the parental levels; (ii) revertants with SSDH activity still missing, but with the other activities fully repaired; (iii) revertants with no SSDH activity, with GSST partly recovered, but with transport fully repaired. It is suggested that thegab cluster is transcribed bidirectionally from a promoter in thegabD region and that the mutation in strain M-16 may be due to DNA insertion in that region.     

Irradiation of micro-organisms with mono-energetic X-rays; biological consequences of the Auger effect.

The radiation resonance effect reported previously for isolated biomolecules has now for the first time been observed in a cellular system. Dried bacteria, Micrococcus denitrificans, in which TdR in DNA was partially substituted by BUdR, were subjected to mono-energetic X-rays of energies below or above the K-edge for Br. Subsequently, the colony-forming ability was assayed. For photon energy slightly above the K-edge, the lethality/rad was greater than that below the K-edge. This is interpreted in terms of the Auger effect initiated selectively by photo-absorption in constituent Br atoms. The differential absorption of low-energy photons in constituent atoms of DNA is also discussed.     

Subunit structure of the glycoprotein complex of avian tumor virus.

Envelope glycoprotein of avian tumor virus is linked by disulfide bonds in a structure that we have designated VGP to stand for viral glycoprotein. VGP appears to contain one molecule of gp85 and one of gp37. Under nonreducing conditions, VGP is the only glycoprotein component that is stable in the presence of ionic detergent, although in the presence of nonionic detergent two or more VGPs are associated in discrete complexes. The disulfide bonds linking viral glycoprotein are formed before release of virus from infected cells.