Distribution of incorporated, synthetic cytokinins in ribosomal RNA preparations from tobacco callus.

The distribution of incorporated synthetic cytokinins (N(6)-[8-(14)C]benzyladenine ([8-(14)C]bzl(6)Ade) and N(6)[8-(14)C]furfuryladenine ([8-(14)C]fr(6)Ade) in ribosomal RNA prepared from tobacco callus (Nicotiana tabacum L. var. Wis. No. 38) grown in the presence of one of these for 25 or 26 days has been studied. The rRNA of tissue supplied with [8-(14)C]bzl(6)Ade or [8-(14)C]fr(6)Ade was fractionated by methylated albumin-Kieselguhr column chromatography and preparative gel electrophoresis, respectively. In each case about 80% of the incorporated cytokinin was recovered as the ribonucleoside [8-(14)C]bzl(6)A or [8-(14)C]fr(6)A in the rRNA peak after the fractionations. [8-(14)C]fr(6)A was found associated with both the 18S and 25S rRNA components in quantities roughly proportional to their 260 nm absorbance. This pattern of apparently nonspecific association was not affected by prior denaturation of the RNA with formamide.The distribution of [8-(14)C]fr(6)A moieties in mono- and oligonucleotides derived from combined treatment of [8-(14)C]fr(6)Ade-labeled rRNA with ribonuclease T(1) and pancreatic ribonuclease A was measured by fractionating the digest on a DEAE-cellulose column in the presence of 7 m urea and determining the [8-(14)C]fr(6)A content in each fraction. The [8-(14)C]fr(6)A content in the oligonucleotides varied from 46 to 210 mumol/mol of adenosine (A). The mol ratio of [8-(14)C]fr(6)A to A was three to four times greater for oligonucleotides containing uridine or cytidine (AUp or ACp) than for those containing quanosine (AGp).