Methylation and processing of ribosomal RNA in HeLa cells.
The methylation of RNA in HeLa cells has been studied. After incorporation of radioactive methyl-labeled methionine, the cells were fractionated into cytoplasmic, nuclear, and nucleolar fractions. Methylation of high molecular weight RNA is shown to be exclusively in the 45 s ribosomal RNA precursor and takes place in the nucleolus. The methylation of the 45 s RNA apparently occurs close to the growing point of newly synthesized RNA as evidenced by the existence of methylated, partially completed molecules after very short pulse labeling. The methyl-labeled RNA was chased with non-radioactive methionine and the progression of the ribosomal RNA precursors was followed through the cell fractions. The data support the previously published hypothesis that nucleolar 45 s RNA is the precursor to cytoplasmic 18 s RNA and 32 s nucleolar RNA. The 32 s RNA is converted to 28 s RNA, which is then found in the nucleoplasm and is the apparent precursor to cytoplasmic 28 s RNA.
Greenberg
H
H
Department of Biology, Massachusetts Institute of Technology Cambridge, Massachusetts, USA.
Penman
S
S
D002458:Cell Fractionation; D006367:HeLa Cells; D006801:Humans; D008715:Methionine / Q000737:chemistry / Q000378:metabolism; D008745:Methylation; D012335:RNA, Ribosomal / Q000737:chemistry / Q000378:metabolism*
D012335:RNA, Ribosomal; D008715:Methionine