The joint distribution of patterns in random sequences with application to the RC-measure for expressivity

A method previously developed for computation of pattern probabilitiesin random sequences under Markov chain models. We extend thismethod to the calculation of the joint distribution for twopatterns. An application yields the distribution of the rightchoice measure for expressivity and how significance boundsdepend on sequence length. These bounds are used to show thatthe choice of pyrimidine in codon position 3 of Escherichiacoli genes deviates considerably from a general Markov processmodel for coding regions. We also derive some statistical evidencethat this significant deviation is limited to codon position3.     

Vinylglycolate resistance in Escherichia coli.

Escherichia coli K-12 vinylglycolate-resistant mutants have been isolated and characterized. Two of the mutants, JSH 150 and JSH 151, have been determined to be double mutants, lacking both membrane-bound L-and D-lactate dehydrogenases. The lactate transport system is intact in all strains; both radioactive lactate and vinylglycolate are actively taken up. Likewise, the phosphoenolypyruvate-dependent phosphotransferase system for hexose uptake is active. Vinylglycolate, previously shown to inhibit the phosphoenolpyruvate-dependent phosphotransferase system, has very little effect in the double mutants. The extent of vinylglycolate inhibition in other mutants seems directly related to the activity of the lactate dehydrogenases. This indicates that vinylglycolate is oxidized to 2-keto-3-butenoate before inactivating the phosphoenolpyruvate-dependent phosphotransferase system. These results were found in whole cells and confirmed in isolated membrane vesicles.     

Tannic acid-stained microtubules with 12, 13, and 15 protofilaments

Subunit structure in the walls of sectioned microtubules was first noted by Ledbetter and Porter (6), who clearly showed that certain microtubules of plant meristematic cells have 13 wall protofilaments when seen in cross section. Earlier, protofilaments of microtubular elements had been described in negatively stained material, although exact counts of their number were difficult to obtain. In microtubular elements of axonemes, some success has been achieved in visualizing protofilaments in conventionally fixed and sectioned material (8, 10); much less success has been achieved in identifying and counting protofilaments of singlet cytoplasmic microtubules. By using glutaraldehyde-tannic acid fixation, as described by Misuhira and Futaesaku (7), Tilney et al. (12) studied microtubules from a number of sources and found that all have 13 protofilaments comprising their walls. These authors note that "...the number of subunits and their arrangement as protofilaments appear universal...". Preliminary studies of ventral nerve cord of crayfish fixed in glutaraldehyde-tannic acid indicated that axonal microtubules in this material possess only 12 protofilaments (4). On the basis of this observation, tannic acid preparations of several other neuronal and non-neuronal systems were examined. Protofilaments in microtubules from these several cell types are clearly demonstrated, and counts have been made which show that some kinds of microtubules have more or fewer protofilaments than the usual 13 and that at least one kind of microtubule has an even rather than an odd number.     

Inhibition of the Anaerobic Growth of Brochothrix thermosphacta by Lactic Acid

Brochothrix thermosphacta can grow aerobically in the presence of 210 mM l-lactate and anaerobically in its absence at pH values down to at least 5.5. Anaerobic growth is, however, inhibited by l-lactate, the concentration of undissociated lactic acid being the governing factor. Postrigor meat usually contains sufficient lactic acid to select against the anaerobic growth of B. thermosphacta. At least some Lactobacillaceae strains are more resistant to lactic acid and so their growth is favored on vacuum-packaged meat.     

PROPERTIES OF RAT BRAIN HISTIDINE DECARBOXYLASE

Abstract– The properties of histidine decarboxylase ( l -histidine carboxylyase EC 4.1,1.22) have been studied in a whole rat brain homogenate. Optimum pH depended upon substrate concentration; the variations of K _m and V _max were determined as a function of pH. pH values lower than 6.0 caused a loss of enzymic activity; activity was stable at pH values higher than 6.0. Enzyme activity was proportional to temperature in the range 30-45°C; temperature characteristic (μ) and Q₁₀ were determined and thermal inactivation was studied. Addition of pyridoxal 5'-phosphate increased enzyme activity. Dialysis of homogenates against phosphate buffer caused a partial loss of enzyme activity which could be restored by addition of the coenzyme to the incubation mixture. Enzyme activity was inhibited by α-methylhistidine and benzene and was unaffected by α-methyl DOPA. The properties correspond to those of a 'specific' histidine decarboxylase. However, the brain enzyme differs from the corresponding enzyme in peripheral tissues in the inability to achieve a total inhibition of activity by dialysis.     

Isolation and characterization of Bacillus subtilis mutants blocked in the synthesis of pantothenic acid.

We have produced and characterized by physiological and enzymatic analyses pantothenate (pan) auxotrophs of Bacillus subtilis. panB auxotrophs are deficient in ketopantoate hydroxymethyltransferase, whereas panE mutants lack ketopantoic acid reductase. The pan mutations were mapped by phage PBS1-mediated two-factor crosses and found to be located in the interval purE-tre of the genetic map of B. subtilis.     

Analysis of soluble human and mouse interferon-gamma receptors expressed in eukaryotic cells.

The extracellular domains of the human and mouse interferon-gamma receptors were produced in insect Spodoptera frugiperda cells infected with recombinant baculoviruses and in mammalian Chinese-hamster-ovary cells. The receptors expressed in both systems are secreted into the culture medium. Their signal peptides are cleaved off and the proteins show heterogeneity in glycosylation which, however, does not affect the capacity to bind interferon gamma or specific antibodies. The soluble mouse receptors exhibit binding capacities similar to those of cell-surface-anchored receptors, whereas the human receptors exhibit a lower binding capacity. All soluble receptors inhibit the binding of interferon gamma to cellular receptors and neutralize the antiviral activity exerted by interferon gamma. These receptors could therefore be useful for structure/function analyses and in vivo studies.