The neural basis of a sensory filter in the Jamming Avoidance Response: No grandmother cells in sight

Summary The Jamming Avoidance Response (JAR), during which weakly electric fish modulate their electric organ discharge rate in response to a foreign electric signal of nearly the same frequency is strongest for frequency differences (f s) between 3–8 Hz. We have searched for neural correlates of this behavioral specificity. Single unit recordings in the anterior lateral line ganglion (ALLG), the posterior lateral line lobe (PLLL) and the torus semicircularis (TS) ofEigenmannia virescens were made during electrical stimulation simulating jamming by a nearby conspecific.Contrary to previously published reports (Scheich 1974, 1977) we conclude that f specificity does not lie in a single class of receptors or higher-order units in the PLLL tuned to the most effective f s. No tuning is seen at the receptor level of the PLLL. Specificity seems to be a population effect first visible at the level of the torus semicircularis, with individual units responding most strongly to different f s, but with most units tuned to approximately + and-4 Hz. By having cells tuned to a variety of f s but occurring in proportions corresponding to the observed behavior (and the degree to which f s impair electrolocation), animals would be better equipped to carry out other tasks such as detection of relative motion of objects in space and would also be better able to read complex stimuli corresponding to the more usual case of simultaneous jamming from several conspecifics (Partridge and Heiligenberg 1980).Units in the PLLL show slight differences in the timing of their firing to jamming signals presented at a frequency slightly above (+f) the fish's pacemaker frequency compared to those presented at a frequency slightly below (–f) (Scheich 1977). Firing pattern within the beat cycle produced by interaction of the fish's EOD, or an electrical mimic, S₁, and the foreign signal, S₂, is largely unaffected by the field orientation of the jamming signal. In the torus, by contrast, two classes of units are encountered which completely reverse the pattern of their firing within the beat cycle if the sign of the f is reversed. And, unlike the PLLL cells, those in TS respond differentially to different stimulus field geometries. Units of class 1 appear to compare T-unit input from different sites on the body surface (Heiligenberg and Bastian 1980) whereas those of class 2 additionally appear to receive input from E- and I-units in the PLLL. Abbreviations: see MethodsThis study was supported by grants from the National Science Foundation and the National Institutes of Health.     

Protein synthesis induced by infection with packaged lambda dv plasmid

Plasmid λdv or imm²¹dv DNA was joined to a λ arm having a cos site. This recombinant plasmid can be packaged in a λ head, and used to infect Escherichia coli K12 cells. The injected DNA molecules become plasmids in cells. By adding these particles to uv-irradiated uvrA cells, the packageable λdv or imm²¹dv plasmids can be induced to synthesize proteins coded by genes on the plasmid genome. The packageable plasmid system is thus suitable for studying on synthesis and regulation of plasmid-coded biopolymers. Analyses of the dv-coded proteins in gel electrophoreses revealed that among several genes carried on the dv plasmid genome, only those genes that are members of the pRoR-tof-cII-O-P operon can be expressed. Evidence has been presented to show that expression of this operon, which is directly correlated with replication of the genome, is only partially allowed in cells perpetuating the dv plasmid. These observations are discussed in connection with the autorepressor model (D. E. Berg, 1974, Virology62, 224–233; K. Matsubara, 1976, J. Mol. Biol.102, 427–439) that genetically accounts for the control mechanism of plasmid replication.     

Purification and properties of a lambda operator-binding protein which is expected to be autorepressor (tof protein) from E. coli carrying lambdadv plasmid.

Summary In order to study the mode of action of the tof gene product, which is an autorepressor of the bacteriophage and plasmid dv, we have purified a DNA-binding protein which is specifically produced in bacteria carrying dv. This protein possesses characteristics expected for the product of the tof gene, since it is produced under conditions where cI-repressor is not made, and since it binds to oL and oR operators on the phage genome. The molecular weight of the native protein is 16,000–17,000 daltons, and the monomeric molecular weight as measured by gel electrophoresis in the presence of sodium dodecyl sulfate is about 10,000 daltons. Denaturation and renaturation experiments demonstrated that the native protein is a dimer of 10,000-dalton monomers. The DNA-specific binding protein is not produced in cells carrying i ²¹dv or 80dv.     

Disulfide bonds of purothionine, a lethal toxin for yeasts.

Purothionin isolated from commercial wheat flour contained several components and two of them (A-I and A-II) were isolated in pure form by CM-52 column chromatography. Each component contained 45 amino acid residues with a 4 disulfide bonds. Purothionin A-II was digested with trypsin and thermolysin to isolate cystine peptides. These were separated and purified by chromatography on an SP-Sephadex column, and paper electrophoresis and chromatography. A peptide containing a -Cys-Cys- sequence was hydrolyzed with 10 N sulfuric acid. Amino acid compositions and partial sequence studies of the cystine peptides and their performic acid-oxidized peptides revealed the positions of all 4 disulfide bonds in purothionin A-II. They were formed between residues 3 and 39, 4 and 31, 12 and 29, and 16 and 25. The results of a partial study of purothionin A-I are also presented.     

X-ray analysis of ferredoxin from Spirulina platensis. II. Chelate structure of active center.

A chloroplast-type ferredoxin from Spirulina platenis crystallized in an orthorhombic system, space group C2221, with cell dimensions a=62.32, b=28.51, and c=108.08 A. The electron density map at 2.8 A resolution was prepared by using the best phase angles determined by the single isomorphous replacement method coupled with the anomalous dispersion method. The chelating structure of the acitve center was revealed as follows. Of the six cysteinyl residues in the molecule, Cys 41, Cys 4k, Cys 49, and Cys 79 are involved in the active center. Cys 41 and Cys 46 are coordinated to one iron atom, and Cys 49 and Cys 79 to the other iron atom. Only one of these cysteinyl residues, Cys 79, is comparatively apart from the other three in the amino acids sequence of the molecule, as found in the case of bacterial ferredoxin. It appears that the NH....S hydrogen bonds are around the active center, as in other non-heme iron sulfur proteins.     

The amino acid sequence of ferredoxin from the alga Mastigocladuslaminosus

Ferredoxin was purified from the thermophilic blue-green alga, Mastigocladuslaminosus. The physicochemical properties of this ferredoxin are similar to those of other [2Fe-2S] plant ferredoxins except for its unusual thermal stability. The primary structure of the protein was determined and consists of 98 amino acid residues, 5 of which are cysteines. The positions of 4 cysteines which bind the iron atoms of the active centre are identical to those in other ferredoxins. The primary structure of the ferredoxin does not reveal any special features to account for its high thermal stability.     

Pumpkin (Cucurbita sp.) seed globulin III. Comparison of subunit structures among seed globulins of various Cucurbita species and characterization of peptide components

Various Cucurbita seed globulins showed patterns similar toone another on SDS-gel electrophoresis, and ß bandsfor unreduced globulins and , ', and ' bands for reduced ones.On gel electrophoresis in 6 M urea, reduced globulin gave twoacidic and two basic bands. These corresponded to and ' chainsand ₁ and ₂ chains, respectively, identified by two-dimensionalurea-SDS gel electrophoresis. The compositions of the and ßsubunits were proposed. (Received September 8, 1977; )     

Random replication and random assortment model for plasmid incompatibility in bacteria

To understand the incompatibility between two related plasmids, both of which replicate in an autonomous state under a common control mechanism, we have developed a model that assumes a random choice mechanism for replication of plasmid copies and their random assortment into daughter cells upon cell division. Segregation kinetics by this model is analyzed mathematically and the number of generations required for segregation is calculated as a function of plasmid copy number per cell. The results obtained offer enough quantitative data to make our model reasonably realistic.     

Role of glycosaminoglycans in the regulation of T cell proliferation induced by thymic stroma-derived T cell growth factor

The present study investigates the regulatory effects of glycosaminoglycans such as heparin and heparan sulfate on T cell proliferation induced by thymic stromal cell monolayer or its derived T cell growth factor (TCGF). A thymic stromal cell clone (MRL104.8a) supported the growth of Ag-specific, IL-2-dependent Th cell clone (9-16) in the absence of Ag and IL-2 by producing a unique TCGF designated as thymic stroma-derived T cell growth factor (TSTGF). The addition of heparin to cultures in which the growth of 9-16 Th cells was otherwise stimulated by the MRL104.8a monolayer or a semipurified sample of the TSTGF resulted in heparin dose-dependent inhibition of 9-16 Th proliferation. The dose of heparin required for inducing 50% reduction of TSTGF-induced proliferation of Th at a given cell number was found to be proportional to the magnitude of the TSTGF added to cultures, suggesting that heparin exerted its inhibitory effect by binding to the TSTGF rather than by acting on Th cells. A similar growth-inhibiting effect of heparin was observed in IL-7-dependent proliferation of pre-B cell line or Th, but not in IL-2-dependent T cell proliferation or IL-3-dependent myeloid cell proliferation. A strong affinity of TSTGF and IL-7 for heparin was confirmed by the fact that both TSTGF and IL-7 adhered to columns of heparin-agarose and were eluted by salt. When various glycosaminoglycans were tested for the heparin-like Th growth-regulatory capacity, heparan sulfate exhibited Th growth-inhibiting ability comparable to that observed for heparin. These results indicate that the activity of thymic and/or bone marrow stroma-derived lymphocyte growth factor (TSTGF/IL-7) but not of Th-producing TCGF (IL-2) is negatively regulated by heparin or heparan sulfate, which would represent major glycosaminoglycans in the extra-cellular matrix of stromal cells.     

Primary structure of a 15-kDa protein from rat intestinal epithelium. Sequence similarity to fatty-acid-binding proteins

An abundant and novel cytosolic protein was purified from the rat intestinal epithelium by gel filtration, ion-exchange and hydroxylapatite chromatography. The protein was eluted into two different positions (fractions 1 and 2) on DEAE-cellulose chromatography. We have completed the primary structure of the protein of fraction 1 by Edman degradation. The protein (144565 Da) contains 127 amino acid residues and has an acetylated alanine at its NH2-terminus. Comparison of the primary structure of the protein with porcine gastrotropin [Walz, A. D., Wider, M. D., Snow, J. W., Dass, C. & Desiderio, D. M. (1988) J. Biol. Chem. 263, 14189-14195] and rat hepatic fatty-acid-binding protein revealed that identical residues within these proteins are found in 90 and 54 out of a total of 127 positions, respectively. Bioactivity studies demonstrated that neither the protein nor liver and intestinal fatty-acid-binding proteins influence gastric acid secretory activity in rats with gastric fistulas compared to pentagastrin. The protein showed very low affinity for palmitic-acid-binding in vitro assay system and only trace amounts of endogenous fatty acids were detected from the protein. The protein, rat intestinal 15-kDa protein is considered to be a new member of the fatty-acid-binding protein family based on its structural features.