Valine-sensitive acetohydroxy acid synthases in Escherichia coli K-12: unique regulation modulated by multiple genetic sites.

Summary Spontaneous mutants (146) of Escherichia coli K-12 were selected that were resistant to inhibition of growth by 1.2 mM L-valine (Val^r). The Val^r isolates, containing acetohydroxy acid synthase resistant to feedback inhibition by L-valine (AHAS^r), were classed according to cotransduction of the mutation with leu. Several mutations resulting in an AHAS^r phenotype were found to be cotransducible with glyA. However, no mutations causing a Val^r phenotype were linked to ilv. AHAS activity was more closely examined in representatives of three classes of mutants with Val^r linked to leu, labeled ilv-660, ilv-661, and ilv-662. The ilvE503 allele in E. coli K-12, known to cause a two- to three-fold derepression of AHAS, was found to affect regulation of synthesis of both valine-sensitive AHAS (AHAS^s) and AHAS^r in the mutants containing ilv-660 and ilv-661, whereas it affected repression of AHAS^s, only, in the mutant containing ilv-662. Further, both AHAS^s and AHAS^r in the ilv-661 mutant were repressed by valine, whereas valine did not repress AHAS^r synthesis in the strain carrying ilv-660 and only partially repressed AHAS^r in the strain carrying ilv-662. Unexpectedly, AHAS^r synthesis in strains carrying ilv-660 or ilv-662 was repressible by leucine. The ilv-660 locus appears to be similar in position to ilvH and encodes a product that confers valine-sensitivity upon AHAS activity in the wild-type E. coli K-12. The ilv-660 and ilv-662 loci may normally encode products that influence both the feedback sensitivity of AHAS and control of AHAS biosynthesis.     

Effects of salinity,temperature and nitrogen fertilization on growth and composition of Rhodes grass (Chloris gayana Kunth.)

The effects of salinity, temperature, and N-fertilization on growth and yield of Rhodes grass were investigated. High levels of all three factors had a negative effect on tillering and consequently on the total yield. Though high salt-stress lowered the yields, it also lowered the content of free-NO₃ ^– in the shoots, thus, raising the quality of the crops obtained.In partial fulfillment of the requirements for the degree of M.Sc. at The Tel Aviv University.In partial fulfillment of the requirements for the degree of M.Sc. at The Tel Aviv University.     

Leaf pretreatment with senescence retardants as a basis for oat protoplast improvement

Protoplasts obtained from oat leaves floated on buffer for 18hr show high nuclease activity, low rates of incorporation ofamino acids and nucleosides into macromolecules, and high ratesof spontaneous lysis. Addition to the leaf flotation mediumof the senescence retardants cycloheximide or kinetin, of thedibasic amino acids L-lysine or L-arginine, or of the diaminesputrescine or cadaverine reduces the rise in nuclease activityand spontaneous lysis of protoplasts, and increases the rateor extent of presumptive protein and nucleic acid synthesis.The diamines, which also retard chlorophyll degradation in theexcised leaves, appear to act both on the membrane and on systemscontrolling macromolecular synthesis and breakdown. By contrast,the senescence promoter L-serine hastens chlorophyll degradationfrom excised leaves and does not improve protoplasts derivedfrom those leaves. (Received July 4, 1977; )     

Seminars in Virology: A Biological Perspective of Slow Virus Infection and Chronic Disease

Sequential events characterize the interaction of viruses with parenchymal cells, and acute lytic infections of tissues and organs have broad biological attributes. A knowledge of these permits a keener understanding of persistent, intermittent herpesvirus infections and persistent, continuous respiratory virus infections. In addition to unique biochemical mechanisms which may permit the latter chronic infections to evolve, the roles of defective and mutant strains of virus, viral interference, and the genetic, developmental and immunological expressions of the host are of considerable and provocative importance.The traditional view of viral infections embraces a broad spectrum of acute pathological and inflammatory events. The relationship of measles virus to subacute sclerosing panencephalitis, the elucidation of the latency of herpes simplex virus, and the slow unmasking of the pathogenesis of multiple sclerosis have illustrated the subtle elements of persistent viral infections of the human being. These chronic neurological diseases have provided the opportunity and stimulus for sharp dissection of the biological and biochemical processes which embellish the logical link of viral infections to other forms of chronic human illness.     

Nucleotide sequence of 5S RNA ofMycobacterium smegmatis

³²P labelled 5S RNA isolated fromMycobacterium smegmatis was digested withT ₁ and pancreatic ribonucleases separately and fingerprinted by two dimensional high voltage electrophoresis on thin-layer DEAE-cellulose plates. The radioactive spots were sequenced and their molar yields were determined. The chain length of the 5S RNA was found to be 120. It showed resemblances to both prokaryotic and eukaryotic 5S RNAs.     

Indigenous and expatriate addicts in Laos: A Comparison

Opium addiction has been reported among virtually all large ethnic groups in Asia. Conspicuous by its absence has been any mention of addiction among the Lao, a people surrounded by poppy-growing tribal groups. A sample of Lao patient-addicts are here compared to expatriate Asian addicts in Laos.Lao and expatriate addicts show marked similarity in their sociodemographic profiles and patterns of narcotic use. Some differences in their recent use of narcotic drugs appear related to the greater cash income of the expatriate Asians and their greater access to heroin. No specifically cultural factors for explaining ethnic differences in addiction have yet been identified.Acknowledgement is expressed to Dr. Charles Weldon, Dr. Chomchan Soudaly, Mr. Larry Berger, and Mr. Boun Ke for their support and assistance in this study. Ms. Grace Peng and Ms. Beth Stone assisted in the tabulation and analysis of the data. The project was supported by the Minnesota Medical Foundation, the International Programs Office at the University of Minnesota, and the National Institute of Drug Abuse (grant no. 5 T01 DA 00023-02 and grant no. 1 R01 DA 01599-01).     

Evidence for a phospholipid requirement of chitin synthase inSchizophyllum commune

Evidence for a lipid dependence of membrane-associated chitin synthase inSchizophyllum commune is based on the following observations: Arrhenius plots of the temperature dependence of this enzyme showed deflections from linearity that are characteristic for lipid-affected membrane-bound enzymes. The activity of chitin synthase dissociated by digitonin decreased at increasing digitonin/protein ratios and could be restored by addition of egg lecithin. After further delipification by sucrose gradient centrifugation, enzyme activity progressively decreased, banded at higher densities, and was less effectively restored by lecithin. The activity of dissociated chitin synthase was also restored by soybean phosphatidylcholine and low concentrations of phosphatidylinositol and phosphatidylserine. At higher concentrations, phosphatidylinositol and phosphatidylserine were inhibitory. Lysophosphatidylcholine and phosphatidylethanolamine were slightly stimulatory, whereas no effect resulting from ergosterol was observed.     

Group mating among Norway rats II. The social dynamics of copulation: Competition,cooperation, and mate choice

The social interactions within groups of Norway rats (Rattus norvegicus) had a strong impact on the individual pattern of copulation which, in turn, affects sperm precedence and the probability of implantation in this species. Males alternated uninterrupted ejaculatory series, augmenting each others' copulatory investment. Females took turns mating after receiving an intromission, collectively potentiating the males' copulatory behaviour; increasing the number of oestrous females increased the number of intromissions and ejaculations achieved by each male but did not affect the amount of copulation experienced by each female. These turn-taking patterns within each sex provided the opportunity to change partners and permitted the emergence of different sex-typical patterns of copulation. Furthermore, the dominant male contributed more intromissions and tended to give each female more ejaculations than the subordinates did. Dominant males were also more likely to inhibit the subordinates' sperm transport. Females competed among themselves for the opportunity to mate with a male as he approached ejaculation and were likely to protect more of the dominant male's sperm transport than the subordinate male's.