Specialized Subregions of the Bifunctional hisB Gene of Salmonella typhimurium

Forty-three hisB mutants of Salmonella typhimurium have been screened to determine the molecular size of the resulting histidinol phosphate phosphatase activity, one of the activities of a bifunctional enzyme produced by this gene which also controls imidazole glycerol phosphate dehydrase activity. Mutation in hisB can lead to the loss of both phosphatase and dehydrase activities, or only of dehydrase activity. Through the use of nonsense mutants lacking dehydrase activity, a distinct point of transition was detected near the middle of hisB at which a dramatic change occurs in the size of the phosphatase enzyme that is synthesized. A missense mutant with a lesion in this region has a high-molecular-weight enzyme which is eluted in the void volume of a Sephadex G-200 column. The enzyme from nonsense mutants near the transition point have molecular weights near 40,000. Even though the buffer conditions are designed to favor the stabilization of the high-molecular-weight form, some mutants have both high- and low-molecular-weight forms. The polypeptide chain specified by the operator proximal part of hisB is sufficient to allow the expression of phosphatase activity. The synthesis of substantially less than the complete product of hisB resulted in association into a form similar to the native enzyme which was found in the void volume of a Sephadex G-200 column.     

Writing in New World Civilizations

Mesoamerican Writing Systems: Propaganda, Myth, and History in Four Ancient Civilizations . Joyce Marcus     

Effects of sampling conditions on selected blood variables of rainbow trout, Salmo gairdneri Richardson

The effects of two methods of specimen immobilization (MS 222 anaesthesia and stunning), two types of anticoagulant (EDTA and heparin), two storage temperature ranges (0–2°C and 22–25°C) and four sample storage periods (0, 1, 3, and 24 h) on the haemoglobin, haematocrit, plasma and packed cell sodium, potassium and chloride ion concentrations and packed cell ATP levels of rainbow trout were examined. Stored samples exhibited increases in cell volume, net transfer of sodium and chloride from plasma into cells, net loss of potassium to plasma and rapid depletion of ATP. Room temperature conditions and prolonged storage exacerbated these changes. Use of EDTA, particularly in combination with MS 222, frequently led to haemolysis. Least change in most variables was observed in samples drawn from stunned specimens, treated with heparin and refrigerated before use or preparation for deep cold storage.     

State-dependent ideal free distributions

Summary The standard ideal free distribution (IFD) states how animals should distribute themselves at a stable competitive equilibrium. The equilibrium is stable because no animal can increase its fitness by changing its location. In applying the IFD to choice between patches of food, fitness has been identified with the net rate of energetic gain. In this paper we assess fitness in terms of survival during a non-reproductive period, where the animal may die as a result of starvation or predation. We find the IFD when there is a large population that can distribute itself between two patches of food. The IFD in this case is state-dependent, so that an animal's choice of patch depends on its energy reserves. Animals switch between patches as their reserves change and so the resulting IFD is a dynamic equilibrium. We look at two cases. In one there is no predation and the patches differ in their variability. In the other, patches differ in their predation risk. In contrast to previous IFDs, it is not necessarily true that anything is equalized over the two patches.     

Molecular packing and intermolecular contacts of sickling deer type III hemoglobin

The X-ray structure of sickling deer type III hemoglobin, solved by the molecular replacement method and refined to an R value of ~25%, has been used to determine the mode of molecular packing and the residues involved in the intermolecular contacts between the hemoglobin tetramers in the crystalline state. The molecules pack in linear arrays (“fibrils”), with adjacent fibrils displaced ~27 Å from one another along the long axis of the arrays. A view down this axis shows an hexagonal network of six fibrils surrounding a central solvent cavity (each hexameric unit is termed a fiber) with adjacent fibers sharing a common wall of fibrils. Contacts less than 5 Å are observed between the following subunits of different molecules: α₁α′₁, α₁α′₂, α₁β′₁, α₁β′₂, α₂β′₁, α₂β′₂, β₂β′₂, in which the primes refer to adjacent molecules.