Nucleotide sequence of nucleolar U3B RNA.

U3A, U3B, and U3C are three distinct molecular weight nucleolar RNAs present in Novikoff hepatoma ascites cells. The primary nucleotide sequence of U3B, the most prominent of these U3 species, was determined. Purified U3B RNA was subjected to various enzymatic digestion procedures, including digests of 32P-labeled U3B RNA, RNA ligase, and polynucleotide kinase labeling, for determination of its primary sequence which is: (formula: see text). The 5'-terminus of the RNA has a "cap" and localized purine-rich regions were found near the 3'-terminus, which have been incorporated into a hydrogen-bonded region in a proposed secondary structure of the molecule.