The rapidly-labeled RNA fraction of E. coli has beenpurified approximately 15-fold on benzoylated DEAE cellulosecolumns (BC). It is metabolically unstable (as shownby a pulse/chase experiment) and is considered to representmRNA. The yield of pulse-labeled RNA is about 70% andcomprises 4-5% of the RNA of the cell.
The true size distribution of this RNA, determined bysedimentation in a denaturing solvent (99% DMSO), does notchange during purification. This result indicates thatneither degradation nor selection for molecules of a particularsize has occurred. Upon sedimentation of the finalpreparation in DMSO, the distribution of pulse label isthe same as that of RNA mass, indicating nearly completeseparation from longer-lived RNA components.
The isolation of globin-specific mRNA from rabbitreticulocytes has been attempted, both by a modificationof BC chromatography and by the previously publishedsucrose gradient method of Marbaix, Burny, and Chantrenne,but the results (in both cases) were inconclusive. Thefinal preparation sedimented heterogeneously, with anestimated mean sedimentation coefficient (s20,w) of 8.4 S.Tests of the possible identity of this material as mRNA bybiological assay in a cell-free protein synthesizingsystem have not been attempted.
