The marine cyanobacterium Synechococcus is the second most abundant phytoplanktonic organism in the world's oceans. The ubiquity of this genus is in large part due to its use of a diverse set of photosynthetic light-harvesting pigments called phycobiliproteins, which allow it to efficiently exploit a wide range of light colors. Here we uncover a pivotal molecular mechanism underpinning a widespread response among marine Synechococcus cells known as "type IV chromatic acclimation" (CA4). During this process, the pigmentation of the two main phycobiliproteins of this organism, phycoerythrins I and II, is reversibly modified to match changes in the ambient light color so as to maximize photon capture for photosynthesis. CA4 involves the replacement of three molecules of the green light-absorbing chromophore phycoerythrobilin with an equivalent number of the blue light-absorbing chromophore phycourobilin when cells are shifted from green to blue light, and the reverse after a shift from blue to green light. We have identified and characterized MpeZ, an enzyme critical for CA4 in marine Synechococcus. MpeZ attaches phycoerythrobilin to cysteine-83 of the α-subunit of phycoerythrin II and isomerizes it to phycourobilin. mpeZ RNA is six times more abundant in blue light, suggesting that its proper regulation is critical for CA4. Furthermore, mpeZ mutants fail to normally acclimate in blue light. These findings provide insights into the molecular mechanisms controlling an ecologically important photosynthetic process and identify a unique class of phycoerythrin lyase/isomerases, which will further expand the already widespread use of phycoerythrin in biotechnology and cell biology applications.light regulation | marine cyanobacteria | phycobilisomes | fluorescence | liquid chromatography-mass spectrometry

We study a dynamic scheduling problem for a multi-class queueing network with a large pool of statistically identical servers. The arrival processes are Poisson, and service times and patience times are assumed to be exponentially distributed and class dependent. The optimization criterion is the expected long time average (ergodic) of a general (nonlinear) running cost function of the queue lengths. We consider this control problem in the Halfin-Whitt (QED) regime, that is, the number of servers n and the total offered load r scale like n ≈ r +ρ √ r for some constantρ. This problem was proposed in [Ann. Appl. Probab. 14 (2004) 1084-1134, Section 5.2].The optimal solution of this control problem can be approximated by that of the corresponding ergodic diffusion control problem in the limit. We introduce a broad class of ergodic control problems for controlled diffusions, which includes a large class of queueing models in the diffusion approximation, and establish a complete characterization of optimality via the study of the associated HJB equation. We also prove the asymptotic convergence of the values for the multi-class queueing control problem to the value of the associated ergodic diffusion control problem. The proof relies on an approximation method by spatial truncation for the ergodic control of diffusion processes, where the Markov policies follow a fixed priority policy outside a fixed compact set.

Endoscopic procedures may be considered an acceptable alternative in children with DWM. The authors propose a treatment protocol based on preoperative MR imaging findings of associated aqueductal stenosis.

This paper studies the eigenvalue problem on R d for a class of second order, elliptic operators of the form L f = a ij ∂ xi ∂ xj + b i ∂ xi + f , associated with non-degenerate diffusions. We show that strict monotonicity of the principal eigenvalue of the operator with respect to the potential function f fully characterizes the ergodic properties of the associated ground state diffusion, and the unicity of the ground state, and we present a comprehensive study of the eigenvalue problem from this point of view. This allows us to extend or strengthen various results in the literature for a class of viscous Hamilton-Jacobi equations of ergodic type with smooth coefficients to equations with measurable drift and potential. In addition, we establish the strong duality for the equivalent infinite dimensional linear programming formulation of these ergodic control problems. We also apply these results to the study of the infinite horizon risk-sensitive control problem for diffusions, and establish existence of optimal Markov controls, verification of optimality results, and the continuity of the controlled principal eigenvalue with respect to stationary Markov controls.

Phycobiliproteins are water-soluble, light-harvesting proteins that are highly fluorescent due to linear tetrapyrrole chromophores, which makes them valuable as probes. Enzymes called bilin lyases usually attach these bilin chromophores to specific cysteine residues within the alpha and beta subunits via thioether linkages. A multiplasmid coexpression system was used to recreate the biosynthetic pathway for phycobiliproteins from the cyanobacterium Synechococcus sp. strain PCC 7002 in Escherichia coli. This system efficiently produced chromophorylated allophycocyanin (ApcA/ApcB) and ␣-phycocyanin with holoprotein yields ranging from 3 to 12 mg liter ؊1 of culture. This heterologous expression system was used to demonstrate that the CpcS-I and CpcU proteins are both required to attach phycocyanobilin (PCB) to allophycocyanin subunits ApcD (␣ AP-B ) and ApcF (␤ 18 ). The N-terminal, allophycocyanin-like domain of ApcE (L CM 99 ) was produced in soluble form and was shown to have intrinsic bilin lyase activity. Lastly, this in vivo system was used to evaluate the efficiency of the bilin lyases for production of ␤-phycocyanin.