Immunological and Biophysical Separation of Dengue-2 Antigens

Antigenic compositions of slowly sedimenting dengue-2 hemagglutinin (SHA) and soluble complement-fixing antigen (SCF) were compared with the virion (rapidly sedimenting hemagglutinin, RHA) by radioimmune precipitation (RIP), RIP inhibition, kinetic neutralization, and neutralization blocking tests with the use of hyperimmune mouse ascitic fluids. RHA and SHA were unable to inhibit completely the RIP of each other by anti-RHA, and neutralization by anti-RHA was not blocked by SHA. This indicated that SHA is serologically related, but not identical, to RHA. SHA differed from RHA in that SHA lacked the “core” polypeptide but contained the two envelope polypeptides. In addition, SHA contained a polypeptide with a molecular weight of 16,500 daltons and a suggestion of several other proteins. These data, when considered with other evidence, suggest that SHA is a special form of “incomplete virus.” SCF was unable to inhibit the RIP of SHA or RHA or to block neutralizing antibodies. Further, anti-SCF did not neutralize RHA or precipitate significant levels of SHA or RHA. Polyacrylamide gel electrophoresis separated SCF from structural polypeptides by molecular size. This evidence suggests that SCF is a nonstructural antigen.     

Inorganic and Metal-Organic Growth Requirements of the Genus Bacteroides

The inorganic and metal-organic growth requirements of ruminal and nonruminal Bacteroides species were compared. The heme requirement of many nonruminal Bacteroides species was similar to that of Bacteroides ruminicola subsp. ruminicola and was a general tetrapyrrole requirement. Some nonruminal Bacteroides species utilized succinate or alpha-ketoglutarate, as well as tetrapyrrole-containing compounds, in place of heme. Fe(+) as well as heme was required for maximal yields of some Bacteroides species. The divalent cation requirements of Bacteroides species are complex. Mg(2+) deletion from a medium containing Mg(2+), Ca(2+), Co(2+), and Mn(2+) reduced the yields of all isolates. Ca(2+) deletion from the same medium reduced the growth yields of Bacteroides fragilis, B. fundiliformis, and one strain of B. oralis. The effects of Mg(2+) and Ca(2+) on the growth of Bacteroides isolates was influenced by other divalent cations. Relatively large quantities of Na(+) were obligately required by all of the currently recognized predominant rumen Bacteroides species. Nonruminal Bacteroides species either did not require Na(+) or required only small amounts. The Na(+) requirement of some nonruminal Bacteroides species could be partially replaced by Li(+) or Cs(+). The Na(+) requirement of rumen Bacteroides species was absolute. The inorganic and metal-organic growth requirements of Bacteroides species appear useful as aids in species differentiation.     

Regulation of Newly Evolved Enzymes. I. Selection of a Novel Lactase Regulated by Lactose in ESCHERICHIA COLI

Thirty-four lactose-utilizing strains of E. coli were selected from a lac Z deletion strain. In 31 of these, the synthesis of the newly evolved lactase is regulated by lactose. The lactase activity in all the strains is indistinguishable from the ebg(+) activity identified by Campbell, Lengyel and Langridge (1973).     

Induction by Mutagens of Tandem Gene Duplications in the glyS Region of the ESCHERICHIA COLI Chromosome

Four mutagens (ultraviolet light, nitrous acid, the acridine half mustard ICR 372, and niridazole) have been found to increase the frequency of tandem gene duplications in the glyS region of the Escherichia coli chromosome. This result was obtained by quantitating the spontaneous and mutagen-induced reversion frequency of a glycyl-tRNA synthetase (glyS) mutant. Following mutagenesis, as many as 0.2% of the survivors were observed to contain duplications in the glyS region. In addition, several classes of stable revertants of the glyS mutant have been identified.     

Fine Structure Mapping, Complementation, and Physiology of ESCHERICHIA COLI hfl Mutants

Six of seven hfl mutations of Escherichia coli K12, characterized by high frequencies of lysogenization by phage lambda and λcIII mutants, are shown to be tightly linked to, but not within, the purA locus. All six hfl mutations are recessive to wild type in hfl⁺/hfl merodiploids and all lie in a single complementation group, located just counterclockwise from the purA locus. All six mutations confer a slightly increased resistance to penicillin and rifamycin and a slightly increased sensitivity to sodium dodecyl sulfate. Some cases of intragenic complementation and intragenic recombination were observed. It is argued that the hfl⁺ gene determines the synthesis of a protein which antagonizes lysogenization by phage lambda. It is further argued that the function of the λcIII gene product is to negate the antagonistic effect of this hfl⁺ protein.     

Restricted pH ranges and reduced yields for bacterial growth under pressure

Hydrostatic pressure was found to cause a marked narrowing of pH ranges for growth and reductions in growth yields for a variety of bacteria. In many cases, reduced yields under pressure could be directly related to increased sensitivities to metabolic acids that accumulated in the enclosed culture vessels used. Magnesium and calcium ions partially reversed increases in sensitivities of representative gram-positive and gram-negative bacteria to low, but not high, pH. Growth inhibition of these organisms at both extremes of pH was associated with enhanced loss of K⁺ from pressurized cells. Inhibited cells in alkaline media also lysed under pressure, but microscopically observable lysis was clearly a secondary phenomenon because it occurred slowly. Apparent volumes for growth-inhibitory protonation-deprotonation reactions were calculated on the basis of measured shifts in inhibitory pH with pressure. The values ranged from 99 to 431 ml/mole, and their magnitudes indicated that growth inhibition by acids or bases involves cooperative changes in polymeric interactions such as those which accompany protein denaturation.     

Equilibrium sedimentation of a polyelectrolyte in a density gradient of a low-molecular weight electrolyte. I. DNA in CsCl

Previous work had indicated that the molecular weight calculated from the equilibrium distribution of DNA in a CsCl density gradient appears to be one half the estimated value of the true molecular weight. In the present study, the sedimentation equilibrium of a polyclectrolyte in a density gradient generated by a low molecular weight electrolyte is treated in terms of the representation according to which a constant fraction of the counterions is considered permanently immobilized and the remaining fraction completely free. Equations for the preferential hydration and the molecular weight are obtained. The validity of the treatment is tested by applying it to experimental data on the equilibrium sedimentation of ?X 174 DNA in CsCl, and it is found that the molecular weight calculated in this way is in agreement with the accepted value for this molecule. Also, recalculation of published data on density gradient centrifugation of T2 DNA in CsCl according to the present treatment brings up the molecular weight to within the range of values given by other methods.