Isolation of a photoreactivation-deficient mutant of Chlamydomonas

A mutant deficient in photoreactivation has been isolated following mutagenesis of Chlamydomonas reinhardi with N-methyl-N'-nitro-N'-nitrosoguanidine. The mutant is deficient in the photorepair of pyrimidine dimers from nuclear DNA but appears to be normal in the rate of photorepair of dimers from chloroplast DNA. Cell-free extracts prepared from the photoreactivation-deficient mutant have about 17% of the DNA photolyase activity of wild-type cells. These results are consistent with the hypothesis that nuclear and chloroplast DNA photolyases are controlled by two separate genes.     

Efficient separation of subfossil Chironomidae from lake sediments

Electron transport system (ETS) activity, CO₂ evolution, O₂ consumption, N₂-fixation (C₂H₂ reduction) and methanogenesis were appropriately measured in aerobic and anaerobically incubated sediment at 4, 10 and 20 ° C to better characterize these activities under different incubation conditions. ETS activity was always higher in the aerobically incubated sediment at all three incubation temperatures, whereas (C₂H₂ reduction was always greater in the anaerobic sediment. Carbon dioxide evolution was detected only in the aerobic sediment at 10 and 20 ° C but not at 4 ° C. Methane evolution in anaerobic sediment increased gradually with an increase in the incubation temperature.     

Binding of [3H]Serotonin to Skeletal Muscle Actin

We previously observed that the neurotransmitter 5-hydroxytryptamine (5-HT, serotonin) binds with high- and low-affinity interactions to an actin-like protein prepared from rat brain synaptosomes. In this study, we examined its binding to highly purified actin obtained from rabbit skeletal muscle. Monomeric G-actin bound serotonin with high and low affinities, exhibiting equilibrium dissociation constants (KD values) of 5 X 10(-5) M and 4 X 10(-3) M, respectively. The serotonin binding site on actin was distinct from those sites previously characterized for divalent cations, nucleotides, and cytochalasin alkaloids. The binding of serotonin (1 microM) to G-actin was increased as much as 26-fold by divalent cations. Potassium iodine (KI) increased the affinity of G-actin for serotonin, KD values for this binding being 3 X 10(-7) M and X 10(-5) M. Serotonin bound with even higher affinity to polymerized F-actin, with KD values of 2 X 10(-8) M and 2 X 10(-5) M. However, the total number of binding sites on F-actin was only about 4% of the number of G-actin. The binding of serotonin (0.1 microM) to G-actin could be inhibited by phenothiazines (1 microM) or reserpine (10 microM), but not by classical antagonists of serotonin receptors or by drugs that release serotonin or inhibit its uptake. The binding of serotonin to actin in vivo may participate in a contractile process related to neurotransmitter release.     

Association of Serotonin, Dopamine, or Noradrenaline with an Actin-Like Component in Pheochromocytoma (PC12) Cells

A rat pheochromocytoma (PC12) cell line was used to examine the possibility that 5-hydroxytryptamine (serotonin), 3,4-dihydroxyphenylethylamine (dopamine), or noradrenaline may be associated with cytoplasmic actin, as was suggested by previous in vitro binding studies on an actin-like protein from rat brain synaptosomes. When PC12 cells were incubated with [3H]serotonin. [3H]dopamine, or [3H]noradrenaline for 30 min at 37 degrees C, approximately 2-4% of the radioactivity present in the cells was found to be associated with a high-molecular-weight (actin-like) component in supernatant fractions. Evidence relating this monoamine binding component to actin filaments includes: (a) its strong absorption by myosin filaments at low ionic strength: (b) a decrease in its affinity for myosin in the presence of 1 mM ATP, which lowers the affinity of authentic actin for myosin: (c) displacement of bound [3H]serotonin from it by DNase I, which binds strongly to actin and which inhibits [3H]serotonin binding to actin in vitro; (d) an increase in its binding of each monoamine (by 25-40%) after PC12 cells were preincubated with 10 microM cytochalasin B (a drug that induces depolymerization of F-actin). These findings suggest that serotonin, dopamine, or noradrenaline may associate with actin filaments in vivo.     

Expression in Bacillus subtilis of the gene for human urogastrone using synthetic ribosome binding sites

Summary A chemically synthesised gene coding for human urogastrone which was earlier cloned in E. coli (Smith et al. 1982) has now been cloned into expression vectors for Bacillus subtilis Two types of constructs have been made, one giving production of methionylurogastrone and the other giving rise to a methionyl-urogastrone- galactosidase fusion polypeptide facilitating quantification of expression levels.The ribosome binding sites used in the expression plasmids are synthetically made oligonucleotides residing on short restriction fragments to allow easy replacement by other ribosome binding sites.Using shuttle vectors and constitutive promoters from Bacillus phages 105 and SPP1, we were able to detect levels of expression amounting to a few thousand molecules per cell during logarithmic growth in both E. coli and B. subtilis.     

Characterization of Cholecystokinin from the Human Brain

Human forms of cholecystokinin have not previously been characterized chemically. In this study, we have extracted and purified the predominant molecular form of cholecystokinin present in human cerebral cortex. The peptide was characterized by amino acid analysis, automated peptide sequencing, and fast atom bombardment mass spectrometry. It appears to be identical to porcine cholecystokinin-octapeptide, with the sequence of Asp-Tyr(SO3)-Met-Gly-Trp-Met-Asp-Phe(NH2). This structural identity is consistent with the observations that the peptide in human brain and porcine cholecystokinin-octapeptide are recognized similarly by a battery of antisera to porcine cholecystokinin; that they coelute from several chromatographic systems, including gel filtration, ion exchange, and reversed-phase; and that they possess similar biological activities.