M25 belongs to the CMV UL25 gene family, and encodes a 130-kDa tegument protein, which is also the most abundant M25 protein with late expression. In addition to the 130-kDa protein, the M25 ORF encodes two other polypeptides of 105 and 95 kDa that are expressed with early kinetics. All three M25 proteins are present in both the nucleus and cytoplasm of infected cells with different relative abundance. It has been shown that M25 protein is present in the nucleus during early stages of infection, following its aggregating around the nucleus and finally accumulation in the cytoplasm during the late phase of infection (Wu, CA et al, Virology. 1999). Data also suggest that M25 is not essential for viral growth in tissue cultures or for viral replication in the salivary glands, lungs, spleens, livers, and kidneys of Balb/c mice (Zhan, X et al, Virology. 2000). Our anti-M25 antibody M25C.01 (described in Scientific Reports volume 7, Article number: 15588 (2017) works in ELISA (on immunogen), IF and FACS (on MCMV infected cells) and each LOT is validated for Western blot (of MCMV infected cell lysates).