Structure of the Tetrahymena pyriformis rRNA gene. Nucleotide sequence of the transcription termination region.

The 3'-terminal regions of the 25 S rRNA and 35 S rRNA were mapped in the HindIIIC fragment of the T. pyriformis rRNA gene (Niles, E. G., and Jain, R. K. (1981) Biochemistry 20, 905-909). The precise locations of these termini were identified by S1 nuclease mapping. The 35 S rRNA was shown to contain two major 3'-ends, one identical to the 3'-end of the mature 25 S rRNA and one which is 15 bases longer. The nucleotide sequence of 440 base pairs of DNA in the terminator region was determined. There are several oligo T stretches and regions of dyad symmetry. Three models of transcription termination are presented which are based on possible secondary structures in the 3'-terminal region of the 35 S rRNA.