Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Sokawa et al. suggest that rel^- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited.     

“Pleiotypic Response”

A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells.     

Electrotonically Coupled Interneurones produce Two Types of Inhibition in <Emphasis Type="Italic">Aplysia</Emphasis> Neurones

IN the abdominal ganglion of Aplysia californica, there are two types of inhibitory post-synaptic potentials (IPSPs). There are unitary short-lasting IPSPs which occur as the result of conductance changes during the movement of Cl^? across the synaptic membrane—IPSPs which have definite equilibrium potentials and characteristics similar to those described for other neuronal systems¹—and there are IPSPs which last much longer and may be much more effective in regulating the activity of the neurone, which Taue has called “inhibitions of long duration” (ILD)^2,3. In Aplysia some of these long lasting inhibitory potentials are produced by conductance changes and have definite equilibrium potentials⁴. Long lasting inhibitions or “slow inhibitory potentials” as well as short lasting IPSPs have also been described in vertebrate sympathetic ganglia⁵, but in these, long lasting IPSPs are not accompanied by changes in membrane conductance. Some of the long lasting inhibitions (LLI) have been explained on the basis of an ATP-dependent electrogenic Na+ pump⁶. Presumably this ATP-dependent pump hyperpolarizes the membrane by causing an outflux of Na+ from the cell which is more rapid than the corresponding “active” influx of K+⁷. There is evidence now for the existence of such an electrogenic Na+ pump in some of the identified neurones of the abdominal ganglion of Aplysia californica⁸. Pinsker and Kandel⁹ have found some evidence that in these neurones the electrogenic Na+ pump is activated by the synaptic action of an identified cholinergic inhibitory interneurone, L10, producing the long lasting “late IPSP”. But Kehoe and Ascher¹⁰, although agreeing that the same interneurone (L10) produces both types of IPSPs in the follower neurones, have shown that the “late IPSP”⁹ is due to an increase in the K+ conductance and that it has an equilibrium potential around ?90 mV. I have found that in this abdominal ganglion there is another specific interneurone which is electrotonically coupled to L10 and which, when activated, produces a long lasting inhibition (LLI) in a number of follower neurones. Thus L10 produces the LLI or “late IPSP” in some follower neurones not directly, but through the mediation of another interneurone.     

Inhibition of DNA Synthesis but not of Poly-dAT Synthesis by the Arabinose Analogue of Cytidine <Emphasis Type="Italic">in vitro</Emphasis>

Kimball and Wilson¹ reported that the arabinose analogue of cytidine (ara-C) inhibited DNA polymerase in a crude extract prepared from Ehrlich ascites cells. Furth and Cohen² observed cytosine arabinoside triphosphate (ara-CTP) inhibited DNA polymerase in extracts from either calf thymus or bovine lymphosarcoma tissue, although these investigators³ had already found no effect of ara-CTP on DNA polymerase from Escherichia coli. The inhibition in both of these cases could be substantially reversed by dCTP; but incorporation of the arabinose nucleotide (ara-CMP) into DNA could not be unequivocally demonstrated. Graham and Whitmore⁴ reported the incorporation of ara-C into DNA in vivo and the inhibition of a DNA polymerase from L cells by ara-CTP. They found that ara-CMP was initially incorporated into small DNA strands but subsequently appeared in long strands. Momparler⁵ has presented evidence that, in vitro, ara-C incorporation was limited to the 3′-hydroxyl end of DNA chains. Such incorporation might be expected to block further chain elongation but this expectation was not supported by the evidence presented by Graham and Whitmore.     

Endopeptidase Activity of Phage λ-Endolysin

JACOB and Fuerst^1,2 demonstrated the presence of a bacteriolytic enzyme (λ-endolysin) in the induced cultures of lysogenic Escherichia coli K12 (λ). The enzyme was later identified as the product of gene R; of phage λ³ which is involved in bacterial lysis at the end of a latent period. The enzyme is apt to form spheroplast-like structures in E. coli² and one would therefore expect its substrate to be murein.     

Induced Bivalent Interlocking and the Course of Meiotic Chromosome Synapsis

WHEN chromosomes pair at meiosis the bivalents so formed do not normally interlock. Heat-treatments can, however, induce bivalent interlocking in the locust Locusta migratoria. Only the longest bivalents interlock and usually only two are found per cell; two “rod” bivalents, with single chiasmata, two “ring” bivalents, each with two or three chiasmata, or one “rod” and one “ring” bivalent (Fig. 1a, b and c). The nature of this interlocking and the metaphase orientational and congressional properties of interlocked bivalents are analysed in detail elsewhere¹.     

New Class of Streptomycin-Resistant Mutants Incompatible with supX Suppressor Mutations in Salmonella typhimurium

Streptomycin-resistant colonies of Salmonella typhimurium appearing in platings of supX suppressors of strain leu-500 are less variegated in size than are those derived from strain leu-500 counterparts. Several of the streptomycin-resistant leu-500 clones, furthermore, yield suppressors and revertants of the leu-500 auxotrophy at unusually low rates, suggesting that they provide a genetic background inimicable to supX suppression. Two such "suppression-restrictive" leu-500 streptomycin-resistant (str) mutants, designated strains M(1) and M(4), were characterized as to their ability to receive the trp-supX-cysB linkage region by transduction. Coentry of a donor supX deletion mutation with the selected trp(+) marker was not observed even though these sites display more than 10% linkage in control experiments. This was demonstrably the result of nonviability of the combined supX mutant, M(1) or M(4) streptomycin-resistant genotype, rather than the lack of suppression of the leu-500 imparted auxotrophy. Both M(1)- and M(4)-type resistance was accompanied by pleiotropic effects resembling those caused by strB (nonribosomal)- rather than strA (ribosomal)-type resistance, but both restrictive mutants had a high upper limit of resistance corresponding to that of strA-type mutants. Transduction analyses indicated that the str character of neither the M(1) nor the M(4) strain was linked to the strA or the strB gene. These mutations define a previously undescribed locus, which we propose to designate strC, apparently related to streptomycin uptake rather than its intracellular action. Mutation at this locus is evidently incompatible with the inactivation or removal of the supX site, suggesting a functional association between products of the genes.