RNA associated with murine intracisternal type A particles codes for the main particle protein

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Abstract
Intracisternal type A particles were isolated from [mouse] MOPC-104E myeloma grown s.c. and from [mouse N4 neuroblastoma cells in culture. Polyadenylated RNA was prepared from the particles and tested in a cell-free translation system derived from rabbit reticulocytes. RNA from the 2 sources directed the synthesis of multiple polypeptides with similar distributions of electrophoretic mobilities in sodium dodecyl sulfate-containing polyacrylamide gels, including 1 component of the same size as the major A-particle structural protein (73,000 daltons). Analysis of the RNA by electrophoresis in methyl mercury-containing agarose gels revealed a 35S component common to A-particles from both cell types. This was a major component of the N4 preparations, but a 28S species predominated in the case of MOPC-104E. These 2 RNA (35S from N4 cells and 28S from MOPC-104E), when isolated on isokinetic sucrose gradients, each directed the synthesis of a 73,000 MW polypeptide that comigrated on gels with authentic A-particle structural protein. Identity of the cell-free product was confirmed by 2-dimensional analysis of the [35S]methionine-labeled tryptic peptides. The N4 RNA preparations also contained a major 32S component which did not code effectively for the A-particle structural protein.