Hemolysis determinant common to Escherichia coli hemolytic plasmids of different incompatibility groups

By using cloned deoxyribonucleic acid fragments from the hemolysis determinant of the hemolytic plasmid pHly152 as hybridization probes, a deoxyribonucleic acid segment of about 3.8 megadaltons was identified as a common sequence in several hemolytic (Hly) plasmids of Escherichia coli belonging in four different incompatibility groups. This segment contained the genetic information for the synthesis and secretion of the extracellular toxin alpha-hemolysin of E. coli. With the exception of pSU5, representing a composite plasmid, one part of which seems to be very similar to pHly152, the overall sequence homology of these Hly plasmids with pHly152 seems to be rather restricted. However, the Hly plasmid pSU316 showed sequence homology with pHly152 that did not extend beyond the hemolysis determinant. The two other plasmids, pSU233 and pSU105, also shared homology with pHly152 in the hemolysis determinant as well as in various other parts of this plasmid which did not seem to be directly linked to the hemolysis determinant. This suggests that the hemolysis determinant has spread to presumably unrelated plasmids of E. coli.     

Populations of the spinach wilt pathogen, Fusarium oxysporum f. sp. spinaciae, in the root tissues, rhizosphere, and soil in the field.

Populations of Fusarium oxysporum f. sp. spinaciae in root tissues and rhizosphere soil of diseased spinach plants were higher than in the root tissues and rhizosphere soil of healthy plants. Populations in soil rhizosphere were higher than in nonrhizosphere soil. The fungus populations were very low in the root tissues of the nonsusceptible strawberry, broccoli, chinese cabbage, and mustard grown in the infested field. The populations were low at the beginning of the season, increased, and remained high during the summer, then dropped in the fall. The fungus populations ranged from 1600 to 2600 propagules/g in the top 10 cm of soil, declined sharply between 11 and 20 cm, and were nondetectable between 41 and 60 cm.     

Structure of the yeast ribosomes. Proteins associated with the rRNA.

Polyamines have been shown to bind to doubled stranded regions of rRNA [3]. Therefore, ribosomal proteins that can be cross linked to these molecules in the ribosomes structure must be bound to or located in the vicinity of the RNA. This technique is the first to yield results on the proteins associated with the rRNA in the eukaryotic ribosome where the lack of purified ribosomal proteins does not allow the use of direct binding studies as in bacterial systems. Proteins S7, S10, S13, S21, S22 and S27 in the small subunit and L2/3, L5, L10/12, L19/20, L22, L23, L36/37, L42 and L43' in the large subunit are labelled when cross linked to [14C]spermidine using 1,5-difluoro 2,4-dinitrobenzene and are good candidates to be RNA-binding proteins in ribosomes from Saccharomyces cerevisiae.     

Binding of aminoacyl-tRNA to rat liver ribosomal proteins

Rat liver ribosome treatment with ethanol and 1 M NH₄Cl releases some 31–33 ribosomal proteins. This split protein fraction binds Phe-tRNA, Ac-Phe-tRNA, Met-tRNA_M and f-Met-tRNA_F in the absence of K⁺ and Mg⁺⁺ ions. When the split protein fraction is passed through Sephadex G-100 only six proteins are retained in the column: S10, S14, S15, S19, L35, and L36. The aminoacyl-tRNA binding activity of this protein fraction retained in the Sephadex G-100 column is similar to that of the total split protein fraction, suggesting that the above six proteins, or only some of them, are involved in the binding reaction.     

Lytic enzymes in the autolysis of filamentous fungi

The degrees of autolysis attained by five different genera of filamentous fungi during an incubation period of 60 days, under the same culture conditions were: 87.3% for Penicillium oxalicum; 65.9% for Neurospora crassa; 62.7% for Polystictus versicolor; 51.7% for Aspergillus niger and 23.5% for Nectria galligena. N. crassa, A. niger and P. versicolor reached the end of the autolysis during this incubation period (60 days), whereas P. oxalicum and N. galligena did not.The excretion of the lytic enzymes -N-acetyl-glucosaminidase, -1–3 glucanase, chitinase, invertase and acid phosphatase into the culture medium during growth and autolysis was investigated. The excretion of these enzymes was consistent with the degree of autolysis reached, the maximum excretion belonging to P. oxalicum and the minimum to N. galligena. The N. crassa invertase was excreted into the culture liquid at levels very much higher than the other enzymes studied, and at levels very much higher than the invertases excreted by the other fungi.     

Chemically defined media for growing anaerobic bacteria of the genus Veillonella

A chemically defined medium for Veillonella parvula and V. alcalescens is described. Some nutritional aspects of the two strains used were examined: the optimum concentration of reducing agents, the requirement for amino acids, diamines, vitamins and other growth factors, and the conditions needed for well balanced nutrition.No specific requirements for single amino acids were observed. A combination of l-cysteine, dl-aspartic acid, l-glutamic acid, l-serine and l-tyrosine, promoted growth. In V. alcalescens, serine could substitute both arginine and tryptophan (or histidine). No growth was obtained with ammonium salts as the sole N source.Decarboxylation of l-ornithine, l-lysine and l-arginine was not demonstrated in the Veillonella parvula strain, which required putrescine or cadaverine for growth. Spermine, spermidine, l-lysine, l-ornithine and l-arginine, could not substitute putrescine in Veillonella parvula. Veillonella alcalescens, which does not require putrescine in the medium, was able to decarboxylate l-ornithine while forming putrescine.     

The nature of the voltage-dependent conductance of the hemocyanin channel.

The electrical responses of individual hemocyanain channels in oxidized cholesterol membranes demonstrate that the voltage-dependent conductance of many-chanel membranes arises from two different mechanisms. These are the voltage-dependent redistribution of channels among several discrete single-channel conductance states themselves. The relaxation time for the discrete conductance changes is of the order of seconds nd the relaxation time of the continuous conductance changes is of the order 10(-4) seconds. As salt concentration in the bathing medium is increased, the single-channel conductance first increases lineary and then saturates. The characteristics of the saturation curves suggest that the continuous conductance changes occur at the edges of the channel and that the mean time an ion spends in the channel is 4 nanoseconds...     

On the adjustment of the sex ratio and the gregarious behavior of animal populations.

Ribosome synthesis in bacteria is linked to RNA polymerase synthesis; both synthesis rates depend upon the values of six parameters: (1) fraction of total ribosomes that is functioning, (2) fraction of total RNA polymerase that is functioning, (3) fraction of functioning RNA polymerase engaged in rRNA synthesis, (4) fraction of total protein that is RNA polymerase protein, (5) peptide chain elongation rate, (6) rRNA chain elongation rate. If these parameters are constant in time, then the numbers of both ribosomes and RNA polymerase molecules increase exponentially. It is shown how the rate constant (fractional increase per unit of time) relates to these parameters and how the kinetics of ribosome and RNA polymerase synthesis respond to a change in any of these parameters.