Cytoplasmic RNA from hen reticulocytes, mouse sarcoma 180 ascites cells, rat liver and barley embryos. Their preparation and purification by a standard procedure and characterization by polyacrylamide gel electrophoresis

The 3'-terminal primary structure of five eukaryotic 18S rRNAs determined by the direct chemical method of sequencing. The highly conserved sequences include an invariant region complementary to eukaryotic 5S rRNA

The 3'-terminal sequences of 18S rRNA from chicken reticulocyte, mouse sarcoma, rat liver, rabbit reticulocyte and barley embryo were determined by the direct chemical sequencing method. The regions sequenced show complete homology for the first 73 nucleotides. A sequence 5'-proximal to the m6(2)Am6(2)A residues that is complementary to eukaryotic 5S RNAs is totally conserved. This supports the hypothesis that base-paired interaction between 5S and 18S rRNA, which are present in the large and small ribosomal subunits respectively, may be involved in the reversible association of ribosomal subunits during protein synthesis.

Hybridizable sequences between cytoplasmic ribosomal RNAs and 3 micron circular DNAs of Saccharomyces cerevisiae and Torulopsis glabrata

We have shown that 2.8 and 3.1 micron circular DNA molecules, previously reported to be present in Saccharomyces cerevisiae and Torulopsis glabrata respectively, contain sequences hybridizing to cytoplasmic ribosomal RNAs. In S. cerevisiae the 2.8 micron circular DNA appears to be identical to the rDNA repeating unit from nuclear DNA, both in length (approximately 9000 base pairs) and in the location of the 25, 18 and 5.8S rRNA sequences on the large HindIII fragment (6500 bp) and the presence of the 5S rRNA sequence on the small HindIII fragment. The 3.1 micron molecule from T. glabrata is approximately 2000 base pairs longer than the S. cerevisiae molecule and in addition, one of the HindIII sites lies within the region hybridizing to 25, 18 and 5.8S rRNAs. In S. cerevisiae the 4-5 copies of the 2.8 micron circular DNA molecules per cell, which have an extra-nuclear location, do not appear to be essential for cell viability as in one strain they were undetectable.