title: An electron microscope study of the relative positions of the 4S and ribosomal RNA genes in HeLa cells mitochondrial DNA.
abstract: The 4S RNA genes in HeLa mitochondrial DNA (mtDNA) have been mapped by electron microscopy using the electron-opaque label ferritin. This method is based on the high affinity interaction between the protein, avidin,and biotin. 4S RNA, covalently coupled to biotin, was hybridized to single-stranded mtDNA. The hybrids were then labeled with ferritin-avidin conjugates. The positions of ferritin-labeled 4S RNA genes were determined relative to the rRNA genes on both heavy (H) and light (L) strands of mtDNA. This region was recognized as a duplex segment after hybridization either with rRNA in the case of H strands or with DNA complementary to rRNA in the case of L strands. Our studies suggest that at least nineteen 4S RNA genes are present in the HeLa mitochondrial genome. On the H strand, we have confirmed the nine map positions found in a previous electron microscope mapping study (Wu et al., 1972) and obtained evidence for three additional 4S RNA genes. On the L strand, seven 4S RNA genes have been mapped. The nineteen genes are distributed more or less uniformly around the genome. There is a pair of closely spaced genes, approximately 150 nucleotides apart, on the H strand, and another closely spaced pair on the L strand.
mesh_terms: D002874:Chromosome Mapping; D004272:DNA, Mitochondrial / Q000032:analysis*; D005293:Ferritins; D005796:Genes; D006367:HeLa Cells; D008854:Microscopy, Electron; D009693:Nucleic Acid Hybridization; D012313:RNA / Q000096:biosynthesis*; D012335:RNA, Ribosomal / Q000096:biosynthesis*
chemical_list: D004272:DNA, Mitochondrial; D012335:RNA, Ribosomal; D012313:RNA; D005293:Ferritins