%0 Journal Article %A Mandic, Lana %A Miller, Matthew S. %A Coulter, Corinne %A Munshaw, Brian %A Hertel, Laura %T Human cytomegalovirus US9 protein contains an N-terminal signal sequence and a C-terminal mitochondrial localization domain, and does not alter cellular sensitivity to apoptosis %D 2009 %J Journal of General Virology, %V 90 %N 5 %P 1172-1182 %@ 1465-2099 %R https://doi.org/10.1099/vir.0.008466-0 %I Microbiology Society, %X The human cytomegalovirus (CMV) US2–US11 genomic region contains a cluster of genes whose products interfere with antigen presentation by the major histocompatibility complex (MHC) proteins. Although included in this cluster, the US9 gene encodes a glycoprotein that does not affect MHC activity and whose function is still largely uncharacterized. An in silico analysis of the US9 amino-acid sequence uncovered the presence of an N-terminal signal sequence (SS) and a C-terminal transmembrane domain containing the specific hallmarks of known mitochondrial localization sequences (MLS). Expression of full-length US9 and of US9 deletion mutants fused to GFP revealed that the N-terminal SS mediates US9 targeting to the endoplasmic reticulum (ER) and that the C-terminal MLS is both necessary and sufficient to direct US9 to mitochondria in the absence of a functional SS. This dual localization suggested a possible role for US9 in protection from apoptosis triggered by ER-to-mitochondria signalling. Fibroblasts infected with the US2–US11 deletion mutant virus RV798 or with the parental strain AD169varATCC were equally susceptible to death triggered by exposure to tumour necrosis factor (TNF)-α, tunicamycin, thapsigargin, brefeldin A, lonidamine and carbonyl cyanide m-chloro phenyl hydrazone, but were 1.6-fold more sensitive to apoptosis induced by hygromycin B. Expression of US9 in human embryonic kidney 293T cells or in fibroblasts, however, did not protect cells from hygromycin B-mediated death. Together, these results classify US9 as the first CMV-encoded protein to contain an N-terminal SS and a C-terminal MLS, and suggest a completely novel role for this protein during infection. %U https://www.microbiologyresearch.org/content/journal/jgv/10.1099/vir.0.008466-0