A low copy number cosmid

A low copy number cosmid was constructed by subcloning the pair of cos sites and the kanamycin resistance gene of pcos2EMBL into pGB2. The resulting cosmid, pPR691, has the pSC101 replicon and specifies resistance to kanamycin, spectinomycin, and streptomycin. pPR691 also carries restriction sites suitable for cloning partial Sau3A digests using the strategy of Bates and Swift (P. F. Bates and R. A. Swift, 1983, Gene 26, 137-146). A library of Salmonella typhimurium chromosomal DNA was made using this cosmid and the rfb gene cluster (map position 42) was isolated from this library.     

Disruption of muscle reorganization by lesions of the peripheral nerve in transforming claws of snapping shrimps

We have performed surgical transections on nerves in the transforming claws of snapping shrimps. In normal transformation muscle restructuring occurs, involving degeneration of some fibers and biochemical changes in others. Surgical section of the entire second limb nerve root or of its distal, dorsal branch--both of which contain the motor axons to the closer muscle--prevents muscle restructuring, even though transformation of external claw morphology proceeds. Furthermore, nerve lesions must be performed within a specific time period after transformation has been triggered in order for the effects to be observed. We suggest that transformation involves an early sensitization of the targeted muscle and that this process depends upon an intact nervous pathway within the second nerve root.     

Structural basis for stabilization of Z-DNA by cobalt hexaammine and magnesium cations

In the equilibrium between B-DNA and Z-DNA in poly(dC-dG), the [Co(NH3)6]3+ ion stabilizes the Z form 4 orders of magnitude more effectively than the Mg2+ ion. The structural basis of this difference is revealed in Z-DNA crystal structures of d(CpGpCpGpCpG) stabilized by either Na+/Mg2+ or Na+/Mg2+ plus [Co(NH3)6]3+. The crystals diffract X-rays to high resolution, and the structures were refined at 1.25 A. The [Co(NH3)6]3+ ion forms five hydrogen bonds onto the surface of Z-DNA, bonding to a guanine O6 and N7 as well as to a phosphate group in the ZII conformation. The Mg2+ ion binds through its hydration shell with up to three hydrogen bonds to guanine N7 and O6. Higher charge, specific fitting of more hydrogen bonds, and a more stable complex all contribute to the great effectiveness of [Co(NH3)6]3+ in stabilizing Z-DNA.     

The octamers d(CGCGCGCG) and d(CGCATGCG) both crystallize as Z-DNA in the same hexagonal lattice

Both (dC-dG)₄ and d(CGCATGCG) crystallize in hexagonal lattices and their three-dimensional structure has been solved by x-ray diffraction analysis. Both molecules are found to form Z-DNA, although the fine details of the structure cannot be visualized due to the statistical disordering of the molecules along the c-axis, which is brought about by the symmetry constraints of the space group. This represents the first time in which the unmodified dinucleotide sequences CpAp and TpGp have been found to form Z-DNA in a crystalline lattice.     

Human tolerance to heat strain during exercise: influence of hydration.

This study determined whether 1) exhaustion from heat strain occurs at the same body temperatures during exercise in the heat when subjects are euhydrated as when they are hypohydrated, 2) aerobic fitness influences the body temperature at which exhaustion from heat strain occurs, and 3) curves could be developed to estimate exhaustion rates at a given level of physiological strain. Seventeen heat-acclimated men [maximal oxygen uptake (VO2max) from 45 to 65 ml.kg-1.min-1] attempted two heat stress tests (HSTs): one when euhydrated and one when hypohydrated by 8% of total body water. The HSTs consisted of 180 min of rest and treadmill walking (45% VO2max) in a hot-dry (ambient temperature 49 degrees C, relative humidity 20%) environment. The required evaporative cooling (Ereq) exceeded the maximal evaporative cooling capacity of the environment (Emax); thus thermal equilibrium could not be achieved and 27 of 34 HSTs ended by exhaustion from heat strain. Our findings concerning exhaustion from heat strain are 1) hypohydration reduced the core temperature that could be tolerated; 2) aerobic fitness, per se, did not influence the magnitude of heat strain that could be tolerated; 3) curves can be developed to estimate exhaustion rates for a given level of physiological strain; and 4) exhaustion was rarely associated with a core temperature up to 38 degrees C, and it always occurred before a temperature of 40 degrees C was achieved. These findings are applicable to heat-acclimated individuals performing moderate-intensity exercise under conditions where Ereq approximates or exceeds Emax and who have high skin temperatures.     

The use of larvae or recruits in coral restoration initiatives: Symbiodinium acquisition does not differ between coral life stages in the wild

Active restoration initiatives are increasingly considered in natural resource management. Laboratory‐reared coral larvae and recruits have been proposed for stock production but it is unknown if their use impacts subsequent symbiosis once transplanted to the reef. We exposed laboratory and field settled aposymbiotic recruits (recently settled <1 month) to Symbiodinium in the wild, then analyzed the acquired communities using ITS‐2 sequencing. There was no significant difference between treatments based on overall community and diversity metrics, or differential abundance of individual taxa. These results suggest that early acquisition is analogous and thus supports the use of either life‐stage as an option for reef restoration.