When
poly(A) sepharose (prepared according to previously published procedures) was stored in aqueous
buffer at 4 degrees C for 5 days or longer, it bound nonspecifically a high percentage of the input
RNA which could not be eluted with
formamide. We have found that treatment with
ethanolamine, followed by
dehydration with
ethanol yielded
poly(A) sepharose which was stable for many months and possessed a low degree of nonspecific binding. Chromatography on
poly(A) sepharose permitted the specific isolation of that fraction of Friend erythroleukemic cell
heterogeneous nuclear RNA (
hnRNA) which contained
oligo(U) sequences. Approximately 10% of the
hnRNA which contained a
poly(A) sequence [
poly(A+)] also contained an
oligo(U) sequence. Interestingly, prior HCHO denaturation of the
hnRNA enhanced binding of the
poly(A+)
oligo(U+)
hnRNA to
poly(A) sepharose by tenfold. This suggested that the
oligo(U) sequence may be in a region with secondary structure, possibly an intramolecular duplex with the 3'
poly(A). Friend cell
oligo(U) sequences ranged from 20 to 50
nucleotides in length and, thus, were similar to the
oligo(U) sequences which heretofore had only been shown to be present in HeLa cell
hnRNA. These results established that rodent cell
hnRNA contain
oligo(U) sequences and demonstrate, for the first time, that
hnRNA containing both a
poly(A) and an
oligo(U) sequence can be separated from other classes of
hnRNA. In addition, conditions are presented for the removal of HCHO from
nucleic acid.