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905 This Letter is devoted to the optical anisotropy arising in a moving medium, where the velocity of light propagation depends on the velocity and direction of motion of the medium. In a rotating medium, the light trajectory is curved The transverse entrainment can be observed for radiation propagating in a rotating optical disk (OD). In 1977, Bilger and Stowell [2] performed an experiment with light propagating in a rotating OD arranged in a laser ring interferometer. The results were interpreted in terms of the Fizeau effect. However, since the rotating disk features a tangential discontinuity of the light propagation velocity on the flat surface, the phase shift in circulating electromagnetic waves was related to both longitudinal and transverse entrainment of the wave. This is confirmed by calculations based on a solution to the dispersion equation, which show that an additional shift of the interference pattern in such experiments can amount to about 20% of the value due to the longitudinal Fizeau effect Below, we consider the results of interferometric experiments in which the optical anisotropy of light propagating in a rotating transparent medium has been studied as a function of the rotation speed. Here, by the optical anisotropy we imply the dependence of the velocity of light on the velocity and direction of motion of the medium where it propagates. The entrainment of light in a moving medium was studied using an interferometer, in which the light was introduced via a flat surface of a rotating OD In the proposed scheme, the beam of laser L is divided by beam splitter BS into two beams. These beams are directed by mirrors M 1 and M 2 so as to pass via the OD in opposite directions. As a result of the OD rotation, one beam acquires a positive, and the other beam, a negative phase shift. Then, the two beams are mixed in the BS, and the mixed beam directed by mirror M 3 passes through optical system OS and strikes photodetector PD. Reversal of the direction of OD rotation leads to a change in the direction of the shift of interference fringes observed in the aperture plane of the PD. The optical path length in the OD was increased due to the multiple reflection of beams from mirror flat surfaces (the front flat surface was mirror coated in the central part, and the rear surface was entirely mirror coated). To the first approximation, the proposed scheme is equivalent to a one-pass Fizeau interferometer. Let us Abstract -We consider the first results of measurements of the effect of a velocity vector field in a rotating transparent medium on the light propagation velocity c in this medium. Laser radiation with a wavelength of λ = 0.632991 µ m passed through a rotating optical disk with n = 1.7125 in an interferometer, where the beam path length projected on the flat disk surface was l = 30.4 mm, the disk thickness was d = 20 mm, and the angle of light incidence on the flat disk surface was ϑ 0 = 50.7 ° . The disk rotation speed was varied up to 380 Hz, which corresponded to a projection of V 2 n = 36 m/s of the medium velocity onto the wave vector of the electromagnetic wave. The experimental data confirmed to the first approximation the classical linear dependence of the shift of interference fringes on the velocity of a rotating medium

Pichia pastoris regulates its gene-specific response to different carbon sources at the transcriptional, rather than the translational, level

Background: The methylotrophic, Crabtree-negative yeast Pichia pastoris is widely used as a heterologous protein production host. Strong inducible promoters derived from methanol utilization genes or constitutive glycolytic promoters are typically used to drive gene expression. Notably, genes involved in methanol utilization are not only repressed by the presence of glucose, but also by glycerol. This unusual regulatory behavior prompted us to study the regulation of carbon substrate utilization in different bioprocess conditions on a genome wide scale. Results: We performed microarray analysis on the total mRNA population as well as mRNA that had been fractionated according to ribosome occupancy. Translationally quiescent mRNAs were defined as being associated with single ribosomes (monosomes) and highly-translated mRNAs with multiple ribosomes (polysomes). We found that despite their lower growth rates, global translation was most active in methanol-grown P. pastoris cells, followed by excess glycerol- or glucose-grown cells. Transcript-specific translational responses were found to be minimal, while extensive transcriptional regulation was observed for cells grown on different carbon sources. Due to their respiratory metabolism, cells grown in excess glucose or glycerol had very similar expression profiles. Genes subject to glucose repression were mainly involved in the metabolism of alternative carbon sources including the control of glycerol uptake and metabolism. Peroxisomal and methanol utilization genes were confirmed to be subject to carbon substrate repression in excess glucose or glycerol, but were found to be strongly de-repressed in limiting glucose-conditions (as are often applied in fed batch cultivations) in addition to induction by methanol. Conclusions: P. pastoris cells grown in excess glycerol or glucose have similar transcript profiles in contrast to S. cerevisiae cells, in which the transcriptional response to these carbon sources is very different. The main response to different growth conditions in P. pastoris is transcriptional; translational regulation was not transcript-specific. The high proportion of mRNAs associated with polysomes in methanol-grown cells is a major finding of this study; it reveals that high productivity during methanol induction is directly linked to the growth condition and not only to promoter strength