FIG. 10.

pUL138 is a type I membrane protein that is not packaged in the virus particle. (A) Schematic of secondary envelopment and egress of HCMV particles. A hypothetical virion particle illustrating the proposed orientation of pUL138 and MHC-I if these Golgi-localized proteins were incorporated into the virus envelope is shown. The chart illustrates the known sensitivities of MHC-I and pUL138 in microsomal membranes, the known sensitivity of pp71 in virions, and the proposed sensitivities of MHC-I and pUL138 in virions to tryptic digestion. (B) Extracellular virions were purified by centrifugation through a sorbitol cushion, followed by banding on glycerol-tartrate gradients. Virions were treated with trypsin at a 20:1 protease-to-protein ratio in the presence or absence of 1% Triton X-100, and 5 μg of protein per lane was analyzed for the presence of pUL138, pp71, and MHC-I by immunoblotting using rabbit anti-UL138 (5484), mouse anti-pp71, and mouse anti-MHC-I antibodies, respectively. Results from two of four independent experiments are shown. A lysate of FIXwt-infected cells was included as a positive control.