The nucleotide sequence of nuclear U6 (4.7 S) RNA

The low molecular weight RNA species which have been purified and characterized in this laboratory (T.S. Ro-Choi and H. Busch (1974) in The Cell Nucleus, Vol. 3, pp 151-208; Academic Press, New York) are now of interest because of their suggested role in processing of heterogeneous nuclear RNAs (Lerner, M.R., Boyle, J.A., Mount, S.M., Wolin, S.L., and Steitz, J.A. (1980) Nature, 283, 220-224). A previously uncharacterized RNA, U6 (4.7 S) nuclear RNA, which is 106 nucleotides long, was extracted from Novikoff hepatoma ascites cell nuclei and purified by polyacrylamide gel electrophoresis. The primary nucleitde sequence of U6 RNA was determined by subjecting the RNA to several types of enzymatic digestions and gel-sequencing techniques. The sequence is: (formula: see text). U6 RNA contains three pseudouridylic acid residues, four alkali-stable dinucleotides, two alkali-stable trinucleotides, one m6adenosine, and one m2guanosine and is notable for the high concentration of modified nucleotides in the center of the molecule. U6 RNA has an unusual 5' terminus which has not yet been fully characterized.