Herpes simplex virions produced by infected human carcinoma No. 2 (HEp-2) cells appear in two general forms, unenveloped (naked) and enveloped. These two forms were separated by zone centrifugation at 18 000 g for 55 min through a 10 to 30% (w/v) sucrose density gradient. The three bands containing virus particles were found by electron microscopy to contain empty naked particles, full naked particles, and enveloped particles. The number of virus particles and the number of plaque-forming units (p.f.u.) were determined for each of the three types of particles. In the band containing enveloped virus particles the infectivity was 1 p.f.u./120 particles; the filled naked particle band yielded 1 p.f.u./60 000 particles; and the empty naked particle band yielded 1 p.f.u./960 000 particles. All of the infectivity of the starting material was recovered from the gradient after centrifugation. It appears that the plaque-forming efficiency of naked virus particles is extremely low, but is not negligible. Particle counts of enveloped full capsids indicate that empty and filled naked particles are enveloped indiscriminately.The infectivity of naked HSV particles as well as the number of naked particles that retain a core is increased when virus is harvested in pH 8.3 medium containing 0.01 M Na citrate, conditions that are unfavorable for DNase activity. The infectivity and morphology of enveloped particles are not affected by this harvesting method.
Naked and enveloped Herpes simplex virus (HSV) particles from infected HEp-2 cells were separated by sucrose density-gradient centrifugation. Infected cells deprived of arginine during the latter half of the virus growth cycle were found capable of synthesizing about the same total number of naked particles as were infected cells maintained in normal medium throughout the cycle. The formation of full capsids in arginine-deprived cells was greatly depressed. The number of enveloped virus particles in the arginine-deprived culture was one-half that of the normal culture, but those full capsids which were enveloped in both cultures were equally infectious.Evidently late arginine deprivation affects the maturation of HSV nucleocapsids, rather than the synthesis of capsid protein, and the enveloping process appears to be affected by arginine deprivation as well.
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