The E1 membrane protein of rubella virus (RuV) is a class II membrane fusion protein structurally related to the fusion proteins of the alphaviruses, flaviviruses, and phleboviruses. Virus entry is mediated by a low pH-dependent fusion reaction through E1's insertion into the cell membrane and refolding to a stable homotrimer. Unlike the other described class II proteins, RuV E1 contains 2 fusion loops, which complex a metal ion between them by interactions with residues N88 and D136. Insertion of the E1 protein into the target membrane, fusion, and infection require calcium and are blocked by alanine substitution of N88 or D136. Here we addressed the requirements of E1 for calcium binding and the intracellular location of the calcium requirement during virus entry. Our results demonstrated that N88 and D136 are optimally configured to support RuV fusion and are strongly selected for during the virus life cycle. While E1 has some similarities with cellular proteins that bind calcium and anionic lipids, RuV binding to the membrane was independent of anionic lipids. Virus fusion occurred within early endosomes, and chelation of intracellular calcium showed that calcium within the early endosome was required for virus fusion and infection. Calcium triggered the reversible insertion of E1 into the target membrane at neutral pH, but E1 homotrimer formation and fusion required a low pH. Thus, RuV E1, unlike other known class II fusion proteins, has distinct triggers for membrane insertion and fusion protein refolding mediated, respectively, by endosomal calcium and low pH. IMPORTANCE Rubella virus causes a mild disease of childhood, but infection of pregnant women frequently results in miscarriage or severe birth defects. In spite of an effective vaccine, RuV disease remains a serious problem in many developing countries. RuV infection of host cells involves endocytic uptake and low pH-triggered membrane fusion and is unusual in its requirement for calcium binding by the membrane fusion protein.Here we addressed the mechanism of the calcium requirement and the required location of calcium during virus entry. Both calcium and low pH were essential during the virus fusion reaction, which was shown to occur in the early endosome compartment. R ubella virus (RuV) is a small enveloped single-stranded RNA virus and the sole member of the Rubivirus genus. Rubivirus and alphaviruses together comprise the Togaviridae (for an overview, see reference 1). While alphaviruses are generally transmitted by mosquito vectors, RuV spreads by airborne transmission between humans, the only known host (2). RuV causes a mild childhood disease commonly referred to as German measles (for a review, see references 1 and 3). However, RuV is able to cross the placental barrier, and infection of pregnant women, particularly during the first trimester, can cause miscarriage, stillbirth, or severe fetal malformations known as congenital rubella syndrome (CRS) (1, 4). While vaccination has essentially eliminated RuV disease and CRS in the Ame...

We prove convergence of the full extremal process of the scale-inhomogeneous discrete Gaussian free field in dimension two in the weak correlation regime. The scale-inhomogeneous discrete Gaussian free field is obtained from the 2d discrete Gaussian free field by modifying the variance through a function I : [0, 1] → [0, 1]. The full extremal process converges to a cluster Cox process. The random intensity of the Cox process depends on I (0) through a random measure Y and on I (1) through a constant β. We show that, in law, the random measure, Y , is equal to the Liouville Quantum Gravity measure at sub-critical temperature α = 2σ(0). The cluster process, which only depends on I (1), can be described as atoms of a standard 2d discrete Gaussian free field conditioned to be unusually high.

We continue the study of the maximum of the scale-inhomogeneous discrete Gaussian free field in dimension two that was initiated in [36]. In this paper, we consider the regime of weak correlations and prove the convergence in law of the centred maximum to a randomly shifted Gumbel distribution. In particular, we obtain limiting expressions for the random shift. As in the case of variable speed branching Brownian motion, the shift is of the form CY, where C is a constant that depends only on the variance at the shortest scales, and Y is a random variable that depends only on the variance at the largest scales. Moreover, we investigate the geometry of highest local maxima. We show that they occur in clusters of finite size that are separated by macroscopic distances. The poofs are based on Gaussian comparison with branching random walks and second moment estimates.

We prove convergence of the full extremal process of the two-dimensional scale-inhomogeneous discrete Gaussian free field in the weak correlation regime. The scale-inhomogeneous discrete Gaussian free field is obtained from the 2d discrete Gaussian free field by modifying the variance through a function I : [0, 1] → [0, 1]. The limiting process is a cluster Cox process. The random intensity of the Cox process depends on the I ′ (0) through a random measure Y and on the I ′ (1) through a constant β. We describe the cluster process, which only depends on I ′ (1), as points of a standard 2d discrete Gaussian free field conditioned to be unusually high.