A modified nucleotide in the poly(A) tract of maize RNA

poly(A)+ RNA was isolated from maize by affinity chromatography on columns of oligo(dT)-cellulose. A modified nucleotide ('X') was detected in ribonuclease T2 digests of the RNA as part of a resistant dinucleotide. The dinucleotide was detected by means of the polynucleotide kinase-mediated transfer of a radioactive phosphate atom from adenosine triphosphate to the 5'-OH position of the dinucleotide. Intact poly(A) tracts were released from poly(A)+ RNA by digestion with ribonuclease T1 and A in a high salt buffer and were isolated by oligo(dT)-cellulose chromatography. The poly(A) preparation was found to consist of a series of polyadenylate fragments which varied in chain length from approximately 17 to greater than 70. The modified nucleotide was shown to occupy an internal position in these poly(A) tracts.