Mediates endoplasmic reticulum to Golgi transport. Together with p115/USO1 and GM130/GOLGA2, involved in vesicle tethering and fusion at the cis-Golgi membrane to maintain the stacked and inter- connected structure of the Golgi apparatus. . [Isoform 2]: Required for Golgi to endoplasmic reticulum retrogade transport, and for intra-Golgi transport. . (Microbial infection) Required for the efficient production of infectious virion during human cytomegalovirus infection. Mechanistically, participates in the formation of the cytoplasmic viral assembly compartment where tegument acquisition and envelopment occur. . This is the function of Ensembl gene identifier ENSG00000162236 (STX5, syntaxin 5).