The effect of reaction with formaldehyde on the sedimentation rates of ribonucleic acids

It has been reported that the RNA of several bacteriophages and that of the larger ribosomal sub-units of mammalian cells sediment faster in the presence of 0·1m-sodium chloride than is expected from their estimated molecular weights. The effect of blocking the hydrogen-bonding amino groups of these and other types of RNA was studied. The RNA of phage R17 no longer sedimented anomalously fast after treatment with formaldehyde. In contrast, the larger ribosomal RNA of HeLa cells appeared more aberrant than before, sedimenting faster than tobacco-mosaic-virus RNA (mol.wt. 2×10⁶) in the presence of formaldehyde. The rapidly labelled nuclear 45s RNA of HeLa cells still sedimented faster than the larger ribosomal RNA after reaction with formaldehyde, showing no evidence of disaggregation. It is suggested that both the large ribosomal RNA and the 45s RNA of HeLa cells may have a non-linear structure.