Binding of a polypeptide antigen to ribonucleic acid from macrophage, HeLa and Escherichia coli cells.

A synthetic branched polypeptide, (T,G)-A-L, formed complexes with RNA which banded at densities lower than that of pure RNA in cesium sulfate gradients after equilibrium centrifugation. In different experiments, the minor bands appeared at densities ranging from 1.56 to 1.63 whereas pure RNA banded at a reproducible density of 1.68. The presence of minor bands was independent of the addition of (T,G)-A-L, but when (T,G)-A-L was added to cell homogenates prior to extraction of RNA, the minute fraction of polypeptide that remained associated with RNA in the gradients was concentrated in the minor bands. The formation of minor bands was independent of the cell type, since they formed to the same extent when peritoneal exudate cells, HeLa cells or E. coli cells were used. Minor bands were not found when RNA was extracted with hot rather than cold phenol. RNA had a pronounced adjuvant effect in priming CSW (responder) mice for immune responses to (T,G)-A-L, but E. coli RNA was at least as effective in this respect as RNA from peritoneal cells. No support was found for the existence of a ribonucleoprotein fraction unique to macrophages.