Inhibition of L1210 tumor growth by thymus DNA

Growth of L1210 leukemia cells which had been previously incubated with thymus DNA was inhibited. Leukemia-cell DNA did not affect tumor growth under similar conditions. Pretreatment of the thymus DNA with deoxyribonuclease suppressed the DNA induced inhibition. Both ribonucleasetreated DNA and untreated DNA inhibited tumor growth.     

Selectivity of intracellular proteolysis: protein substrates activate the ATP-dependent protease (La)

A critical enzyme in protein breakdown in Escherichia coli is protease La (the lon gene product), which hydrolyzes proteins and adenosine triphosphate (ATP) in a coupled process. The mechanism of this process was studied with fluorogenic tripeptides. Although proteins and peptides are degraded at the same active site, protein substrates enhance the ability of the enzyme to degrade these peptides two- to tenfold. Proteins that are not substrates had little or no effect. Thus, protein substrates must bind to protease La at two sites, the active site and an allosteric site whose occupancy enhances proteolytic activity. This effect did not require that the proteins themselves be degraded. Proteins could induce peptide breakdown even in the absence of ATP, and proteins and ATP had additive effects in stimulating peptidase activity. A multistep cyclical mechanism is proposed in which the binding of the substrate and ATP activates the protease. The enzyme can then cleave a peptide bond, but is inactivated through ATP hydrolysis. Such a mechanism may help account for the selectivity of protein breakdown and prevent inappropriate or excessive proteolysis in vivo.     

Middle Stone Age bedding construction and settlement patterns at Sibudu, South Africa

The Middle Stone Age (MSA) is associated with early behavioral innovations, expansions of modern humans within and out of Africa, and occasional population bottlenecks. Several innovations in the MSA are seen in an archaeological sequence in the rock shelter Sibudu (South Africa). At ~77,000 years ago, people constructed plant bedding from sedges and other monocotyledons topped with aromatic leaves containing insecticidal and larvicidal chemicals. Beginning at ~73,000 years ago, bedding was burned, presumably for site maintenance. By ~58,000 years ago, bedding construction, burning, and other forms of site use and maintenance intensified, suggesting that settlement strategies changed. Behavioral differences between ~77,000 and 58,000 years ago may coincide with population fluctuations in Africa.     

Stabilizing Lead-Salt Diode Lasers: Understanding and Controlling Chaotic Frequency Emission

Lead-salt tunable diode lasers (TDLs) are the only devices currently available that can generate tunable monochromatic radiation at arbitrary wavelengths between 3 and 30 micrometers and are particularly useful for high-resolution spectroscopy over a wide range of spectral regimes. Detailed observations of TDLs show that the observed instrumental linewidth is actually a temporal average of many narrow (less than 0.5 megahertz) emission "modes." The time scale characteristic of these "modes," which appear to be of relatively constant intensity, is of the order of a microsecond. The laser's behavior is highly suggestive of a chaotic process, that is, seemingly random excursions of a dynamic variable (frequency) within a bounded range. This report shows experimentally that TDL emissions are indeed chaotic. Furthermore, in a simple and robust fashion, this chaotic behavior has been successfully controlled with the use of recent techniques that take advantage of chaos to produce a narrow band laser output.     

Morphologies and origin of elemental carbon in the environment

Carbon particles extracted from sediments collected by box coring from southeastern Lake Michigan were compared with carbon particles extracted from oil, coal, and wood fly ash. Sediments deposited after 1900 contained coal, oil, and wood carbons; older sediments contained only wood carbon.     

Lead pollution: records in Southern California coastal sediments

The present anthropogenic lead fluxes into sediments from the Santa Monica, San Pedro, and Santa Barbara basins of Southern California are, respectively, 0.9, 1.7, and 2.1 micrograms of lead per square centimeter of sea bottom per year; the natural (prepollution) rates for these three basins were, respectively, 0.24, 0.26, and 1.0 microgram of lead per square centimeter per year. Studies of isotopic composition indicate that lead pollutants in coastal sediments are derived mainly from the combustion of lead additives in gasoline.     

Neurons in monkey prefrontal cortex that track past or predict future performance

Although frontal cortex is thought to be important in controlling behavior across long periods of time, most studies of this area concentrate on neuronal responses instantaneously relevant to the current task. In order to investigate the relationship of frontal activity to behavior over longer time periods, we trained rhesus monkeys on a difficult oculomotor task. Their performance fluctuated during the day, and the activity of prefrontal neurons, even measured while the monkeys waited for the targets to appear at the beginning of each set of trials, correlated with performance in a probabilistic rather than a determinist manner: neurons reflected past or predicted future performance, much more than they reflected current performance. We suggest that this activity is related to processes such as arousal or motivation that set the tone for behavior rather than controlling it on a millisecond basis, and could result from ascending pathways that utilize slow, second-messenger synaptic processes.