The UFM1 Pathway Impacts HCMV US2-Mediated Degradation of HLA Class I.

To prevent accumulation of misfolded proteins in the endoplasmic reticulum, chaperones perform quality control on newly translated proteins and redirect misfolded proteins to the cytosol for degradation by the ubiquitin-proteasome system. This pathway is called ER-associated protein degradation (ERAD). The human cytomegalovirus protein US2 induces accelerated ERAD of HLA class I molecules to prevent immune recognition of infected cells by CD8+ T cells. Using US2-mediated HLA-I degradation as a model for ERAD, we performed a genome-wide CRISPR/Cas9 library screen to identify novel cellular factors associated with ERAD. Besides the identification of known players such as TRC8, p97, and UBE2G2, the ubiquitin-fold modifier1 (UFM1) pathway was found to affect degradation of HLA-I. UFMylation is a post-translational modification resembling ubiquitination. Whereas we observe ubiquitination of HLA-I, no UFMylation was detected on HLA-I or several other proteins involved in degradation of HLA-I, suggesting that the UFM1 pathway impacts ERAD in a different manner than ubiquitin. Interference with the UFM1 pathway seems to specifically inhibit the ER-to-cytosol dislocation of HLA-I. In the absence of detectable UFMylation of HLA-I, UFM1 may contribute to US2-mediated HLA-I degradation by misdirecting protein sorting indirectly. Mass spectrometry analysis of US2-expressing cells showed that ribosomal proteins are a major class of proteins undergoing extensive UFMylation; the role of these changes in protein degradation may be indirect and remains to be established.

Color-reflection holography: theory and experiment.

We present a theoretical and experimental analysis of color-reflection holography. Full parallax three-dimensional color images are obtained by the superposition of wavelength-selective reflection holograms recorded at eight combinations of three laser wavelengths. The test object used was a set of eight Munsell color chips recommended by the Commission Internationale de l'Eclairage (CIE) for color-rendering analysis. The spectral power distributions of all the holographic images are measured using a telespectroradiometer and corresponding points are calculated and plotted on a color diagram. The holograms are modeled by a combination of sinc functions for the diffracted replay signal and an empirically determined function for the replay scatter noise. A new definition of signal-to-noise ratio for color holograms is described. The model is matched to a spectral power distribution by choosing values for relative diffraction efficiencies, bandwidth, signal-to-noise ratio, and wavelength shift components. One spectral power distribution having been matched, theoretical predictions of the remaining colors in the holographic images are obtained. The predictions mapped on the CIE 1976 diagram are shown to agree with experimental results: the average distance between theoretical and experimental points on the CIE diagram for all eight Munsell chips on all eight holograms is 0.0001 CIE 1976 chromaticity diagram unit; the discrepancy of the average gamut area between theoretical and experimental points on the CIE diagrams was < 10%. Good agreement between theory and experiment having been shown, a synthesis of holographic color reproduction at any combination of wavelengths predicts optimum recording wavelengths of 460, 530, and 615 nm for typical replay by a color-reflection hologram.