Studies on RNA ligase activity in the brain and liver cells of mouse

RNA ligase in eukaryotic mammalian cells was studied by using mouse brain and liver cell extracts as enzyme sources and Oligo A as substrates. RNA ligase activity was determined by measuring the formation of alkaline phosphate-resistant product from 5'-32P-terminated Oligoribonucleotides. Under appropriate conditions, the activity of this enzyme in brain and liver cells may vary between 16-49 mU/ml. The joining way between donor and acceptor is 5'-P----3'-OH. Further studies were carried out by using synthetic UpCpU and 32pNp as substrates and crude enzyme preparations from extracts of cell nuclei of brain and liver as enzyme sources. RNA ligase activity was examined by homochromatography and autoradiography. A clear joining product was demonstrated and then isolated from the reaction mixture by DEAE-Sephadex A25 column chromatography. The eluted fractions were identified by DEAE-cellulose thin layer chromatography. The joining product was hydrolyzed either with KOH or with alkaline phosphatase, the autoradiographic spot of the product disappeared. In this case the joining way between donor and acceptor is 3'-P----5'-OH instead of 5'P----3'-OH. All this indicated that in extracts of mouse brain and liver cells most probably exists some other kind of RNA ligase, which differs from the T4 RNA ligase in the joining way.