The properties and function of parental nucleocapsid-like particles (NLP) in the cytoplasm of Sendai virus-infected Ehrlich tumour cells were studied. The formation of NLP stems from partial uncoating of the virus particles leading to the loss of about 60% of the mol. mass of virus protein, the genome in the NLP being fully conserved. Uncoating proceeds at 37 °C, but not at 0 °C, and does not require the synthesis of protein and host RNA. NLP sedimentation rate (∼ 200S) and buoyant density in caesium chloride (1.34 g/ml) are fairly close to those of nucleocapsids produced by treatment of the virus with sodium deoxycholate. However, the following differences between the two types of structures are found: (i) NLP are sensitive to ribonuclease; (ii) NLP contain the largest virus particle protein in addition to the nucleocapsid protein; (iii) most molecules of parental RNA in NLP sediment slower than RNA of native virus particles (50S), this phenomenon apparently not being due to genome RNA degradation.

The involvement of NLP in the parental genome transcription is deduced from the following observations: (i) NLP possess the RNA polymerase activity ; (ii) virus-induced RNA synthesis can be detected in the infected cells at a stage when all cytoplasmic parental RNA seems to be in NLP; (iii) a part of newly synthesized virus-specific RNA is associated with NLP; the kinetics of labelling suggest that the RNA is synthesized in NLP and released after synthesis.


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