Preparation, molecular weight, base composition, and secondary structure of giant nuclear ribonucleic acid

Previous methods of heterogeneous ribonucleic acid (HnRNA) extraction yield material which "disaggregates" into small molecules. This could be the fault of either ribonuclease knicks in the polymers sustained during the extraction procedure or disaggregation into real subunits. The present communication distinguishes between these possibilities by describing an RNA extraction procedure which does not yield subunits when HnRNA is denatured. By the criteria of sedimentation through sucrose, formaldehyde, and dimethyl sulfoxide, it is estimated that the majority of the radioactivity of giant HnRNA after a 30-min pulse of [³H]uridine is associated with molecules in the range 5-10 × 10⁶ daltons. In the electron microscope, under denaturing conditions, 84% (mass %) of giant HnRNA has a contour length of 4-9 μ corresponding to a molecular weight of about 5-10 × 10⁶. Giant HnRNA has a "DNA-like" base composition (G + C = 46-54%) and has considerable secondary structure (ca. 60% helix conformation) as judged by its melting profile and reactivity with formaldehyde.