The integration of diverse electronic phenomena, such as magnetism and nontrivial topology, into a single system is normally studied either by seeking materials that contain both ingredients, or by layered growth of contrasting materials 1-9 . The ability to simply stack very different twodimensional (2D) van der Waals materials in intimate contact permits a different approach 10,11 . Here we use this approach to couple the helical edges states in a 2D topological insulator, monolayer WTe2 12-16 , to a 2D layered antiferromagnet, CrI3 17 . We find that the edge conductance is sensitive to the magnetization state of the CrI3, and the coupling can be understood in terms of an exchange field from the nearest and next-nearest CrI3 layers that produces a gap in the helical edge. We also find that the nonlinear edge conductance depends on the magnetization of the nearest CrI3 layer relative to the current direction. At low temperatures this produces an extraordinarily large nonreciprocal current that is switched by changing the antiferromagnetic state of the CrI3. Main Text:The introduction of magnetic order into topological band structure gives rise to new phenomena such as the quantum anomalous Hall effect 1,8,9 and nonreciprocal magnetoelectric effects [5][6][7]18 . In the case of a two-dimensional topological insulator (2D TI), topology guarantees the existence of helical edge modes in which the spin is locked to momentum, causing current at the edge to be fully spin-polarized (the quantum spin Hall effect) 19 . Combining 2D TIs with magnets should therefore directly yield magnetoelectric coupling 20,21 . For example, a magnetic proximity effect may modify the spin polarization and hence the current, or the flow of current in the edge may produce a torque on the magnetization 22,23 . Since backscattering in the edge modes is suppressed by time reversal symmetry, the edge conduction should be affected by magnetic order, which will mix the two opposite-spin branches and so modify backscattering. The expected gapping of the helical edge modes by proximity with a ferromagnet is an important way to control them which, combined with induced superconductivity 24,25 , plays a role in schemes to produce Majorana modes 26 .Stacking van der Waals materials offers a simple, flexible and low-disorder approach to combining magnets with other materials 10,11 . In this work we measure transport through a 2D TI, monolayer (1L) WTe2 13-16 , stacked under the layered magnetic insulator CrI3 17,27-30 . We find that the magnetism of the CrI3 suppresses the edge conduction in the WTe2, in a manner consistent with

The inherent stochasticity of cellular processes leads to significant cell-to-cell variation in protein abundance. Although this noise has already been characterized and modeled, its broader implications and significance remain unclear. In this paper, we revisit the noise model and identify the number of messages transcribed per cell cycle as the critical determinant of noise. In yeast, we demonstrate that this quantity predicts the non-canonical scaling of noise with protein abundance, as well as quantitatively predicting its magnitude. We then hypothesize that growth robustness requires an upper ceiling on noise for the expression of essential genes, corresponding to a lower floor on the transcription level. We show that just such a floor exists: a minimum transcription level of one message per cell cycle is conserved between three model organisms: Escherichia coli, yeast, and human. Furthermore, all three organisms transcribe the same number of messages per gene, per cell cycle. This common transcriptional program reveals that robustness to noise plays a central role in determining the expression level of a large fraction of essential genes, and that this fundamental optimal strategy is conserved from E. coli to human cells.