A cyclin-dependent kinase family member (PHOA) is required to link developmental fate to environmental conditions in Aspergillus nidulans

We addressed the question of whether Aspergillus nidulans has more than one cyclin-dependent kinase gene and identified such a gene, phoA, encoding two PSTAIRE-containing kinases (PHOAM1 and PHOAM47) that probably result from alternative pre-mRNA splicing. PHOAM47 is 66% identical to Saccharomyces cerevisiae Pho85. The function of this gene was studied using phoA null mutants. It functions in a developmental response to phosphorus-limited growth but has no effect on the regulation of enzymes involved in phosphorus acquisition. Aspergillus nidulans shows both asexual and sexual reproduction involving temporal elaboration of different specific cell types. We demonstrate that developmental decisions in confluent cultures depend upon both the initial phosphorus concentration and the inoculation density and that these factors influence development through phoA. In the most impressive cases, absence of phoA resulted in a switch from asexual to sexual development (at pH 8), or the absence of development altogether (at pH 6). The phenotype of phoA deletion strains appears to be specific for phosphorus limitation. We propose that PHOA functions to help integrate environmental signals with developmental decisions to allow ordered differentiation of specific cell types in A.nidulans under varying growth conditions. The results implicate a putative cyclin-dependent kinase in the control of development.     

DSIF, a novel transcription elongation factor that regulates RNA polymerase II processivity, is composed of human Spt4 and Spt5 homologs

Twenty-four subjects walked at different speeds (V) from 0.4 to 2.6 m s-1, while motion and ground reaction forces were recorded in 3-D space. The total mechanical energy of each body segment was computed as the sum of the gravitational potential, translation and rotation kinetic energies. Energy profiles reveal that there are inter-individual differences, particularly at moderate and fast V. In some subjects, the energy excursions are less pronounced, and tend to evolve out of phase at the lower limbs and trunk. As a consequence, there is a better transfer of energy between the trunk and the leg segments, resulting in smaller oscillations of the net energy of the whole body. There is a threefold variation of the rate of increment of lnPu (the mass-specific mean absolute power) with lnV across subjects. We show that this variability cannot be simply explained on the basis of the different biomechanical characteristics of the subjects, but that it depends on the different kinematic strategies. Subjects differ in their ability to minimize energy oscillations of their body segments and to transfer mechanical energy between the trunk and the limbs. Individual characteristics of the mechanical energy expenditure were correlated with the corresponding kinematic characteristics. The changes of the elevation angles of the lower limb segments covary along a plane in all subjects. Plane orientation (quantified by the direction cosine of the normal with the thigh axis, u3t) at any V is not the same in all subjects, but correlates with the net power output: smaller values of u3t tend to be associated with smaller values of Pu, and vice versa.     

Solution structure of SpoIIAA, a phosphorylatable component of the system that regulates transcription factor sigmaF of Bacillus subtilis

The establishment of differential gene expression in sporulating Bacillus subtilis involves four protein components, one of which, SpoIIAA, undergoes phosphorylation and dephosphorylation. We have used NMR spectroscopy to determine the solution structure of the nonphosphorylated form of SpoIIAA. The structure shows a fold consisting of a four-stranded beta-sheet and four alpha-helices. Knowledge of the structure helps to account for the phenotype of several strains of B. subtilis that carry known spoIIAA mutations and should facilitate investigations of the conformational consequences of phosphorylation.     

Evidence for a H+ nitrate symporter in Aspergillus nidulans

Nitrate transport in Aspergillus nidulans was dependent upon a consistent proton motive force (delta p) across the cell membrane which was maintained in a range of 105 (+/- 6.7) to 131 (+/- 3.4) mV over an external pH span of 5.5 to 7.5. The membrane potential (delta psi) measured by uptake of [3H]-tetra-phenylphosphonium bromide and the transmembrane pH difference (delta pH) measured by the distribution of 3H2O and [14C]- salicylic acid were used to compute the delta p present during transport of nitrate. Energy dependent accumulation of nitrate was measured in actively assimilating and tungstate inhibited cells. A delta G for nitrate of 14 kJ mol-1 was computed from the results. Cells induced for nitrate transport maintained internal nitrate levels of 6 to 8 mM based on an internal volume of 2.6 microliters/mg dry wt as determined by a conventional dual label procedure. A fivefold higher level of cellular nitrate was observed in tungstate inhibited cells. Nitrate accumulation was dependent upon a H+ gradient which was dissipated by treatment with 2-butanol, the ionophores valinomycin and gramicidin and the proton conductors carbonyl cyanide m-chlorophenyl hydrazone and N,N'-dicyclo-hexylcarbodiimide. Significant ATP and nitrate efflux occurred in cells treated with the above agents. The results suggest that nitrate is transported by symport with H+ on a carrier which is functionally linked to a H+ ATPase pump.