Nuclear ligation of RNA polynucleotide kinase products

RNA polynucleotide kinase has been shown to transfer [gamma 32P] from ATP to 5-OH termini of endogenous nuclear RNA. The products of this reaction have been isolated in RNA larger than 125 after in vitro incubation of mouse L cell nuclei. About 20%-30% of these 5'-OH kinase products are polyadenylated. A sizeable fraction of the [gamma 32P] label from ATP is also found in internal phosphodiester bonds after 30-minute nuclear incubation in vitro. The possibility of substantial [32P] 1) 2mM nucleoside triphosphates in the incubation medium, 2) limited nearest-neighbor distribution 3' and 5' to the phosphodiester bond compared with that from [alpha 32P] UTP, 3) different nearest-neighbor distribution for RNA molecules greater than 125 and 12-3S, 4) relative insensitivity of the [gamma 32P] incorporation to alpha-amanitin as compared with total RNA synthesis, 5) internal [32P] appearance in RNA greater than 12S in less than five minutes of incubation, and 6) less than 0.03% to 0.6% of the total [32P] in the alpha position of nucleoside triphosphates after 30 minutes of incubation. The [gamma 32P] incorporation was dependent on high ATP concentration and was insensitive to competition by inorganic phosphate. These results are consistent with the levels of 5' RNA polynucleotide kinase activity in L cell nuclei and suggest the presence of an RNA ligase that can utilize the termini generated by the 5'-OH RNA kinase in a ligation reaction.