Number of genes and base composition of mitochondrial tRNA from Saccharomyces cerevisiae

Studies on tRNA adaptation, tRNA turnover, precursor tRNA and tRNA gene distribution in Bombyx mori by using two-dimensional polyacrylamide gel electrophoresis

Eighteen out of twenty amino acids have been used for identifying tRNAs from the silkworm Bombyx mori L. fractionated on two-dimensional polyacrylamide gel electrophoresis. 43 spots out of 53 have been identified. This mapping confirms previous results and brings new answers to some questions on the regulation of tRNA biosynthesis. 1. In addition to quantitative adaptation of tRNAs to the composition of silk proteins (fibroin from the posterior silk gland, sericin from the middle part) and of iso-tRNAs from posterior silk gland to the major codons of fibroin mRNA, we also observe adaptation of tRNA from various tissues to the average amino acid content of proteins from fat body, gut, gonads and carcass of the silkworm. 2. In the silk gland, turnover rates of several tRNA species are similar. The selective accumulation of tRNAs needed for decoding fibroin and sericin mRNAs which takes place during the Vth larval instar, cannot be explained by the occurrence of a preferential degradation of some tRNA species. 3. Under given conditions for incubating silk glands, it is possible to obtain an accumulation of precursor tRNA species, which are enriched in pre-tRNAAla and pre-tRNAGly in the posterior silk gland and pre-tRNASer in the middle part. 4. The distribution of tRNA genes is not random. tRNA genes for glycine, alanine and serine are prominent. Selective transcription of batteries of iso-tRNA genes could explain our data.

The genetic map of transfer RNA genes of yeast mitochondria: correction and extension

Ninety five rho- mitochondrial DNA's of Saccharomyces cerevisiae were compared for their deletion structure by means of 15 genetic markers and 22 tRNA genes. The patterns of co-deletion and co-retention of different tRNA genes allowed us to determine their positions with respect to each other. The deduced order of tRNA genes was consistent with the order of the genetic markers established by independent genetic approaches. Our previously proposed mitochondrial tRNA gene map has been revised and extended. Transfer RNA genes, corresponding to all 20 aminoacids, and two isoacceptor tRNA genes were localized. The possible position of each tRNA gene has been indicated on the physical map of mitochondrial DNA. Seventeen tRNA genes are carried by a narrow region representing less than 20% of the wild type genome.

Laboratory of Physiological Chemistry, State University Groningen, Netherlands

To obtain more information about the arrangement of Hind III restriction fragments in the tRNA-rRNA region of the Neurospora crassa mitochondrial (mt) DNA we have cleaved the mtDNA with Hpa I and Hind II. We could construct additional cleavage maps for these enzymes. Hybridization of rRNAs to Hind II fragments confirmed the existence of an intervening region of about 2,300 basepairs in the 24S rRNA (Hahn et al., Cell, in press). About seven tRNA genes, among which the genes for tRNA1Ser and tRNAMetM, are located in a segment of about 5,000 bp separating the 24S and 17S rRNA genes. Another cluster of 14 tRNA genes is found adjacent to the other end of the 24S gene. The genes for tRNALeu1 and tRNAMetF are located in this cluster.

Neurospora crassa mitochondrial transfer RNAs

Total mitochondrial tRNA from Neurospora crassa was characterized by base composition analysis, one- and two-dimensional gel electrophoreses and reversed-phase chromatography on RPC5. The guanosine + cytidine content was about 43%, as compared to 60% for cytoplasmic tRNA. The modified nucleoside content was low and about the same as that of total yeast mitochondrial tRNA, though the G + C content is very different. We found psi, T, hU, t6A, m1G, M2G, m22G. Neither the eukaryotic "Y" base, nor the prokaryotic s4U were present. On two-dimensional polyacrylamide gel electropherograms about 25 species were separated. One species for phenylalanine, two for leucine and two for methionine could be located. Neurospora crassa mitochondrial tRNA does not hybridize with yeast mitochondrial DNA.

Physical mapping of genes on yeast mitochondrial DNA: localization of antibiotic resistance loci, and rRNA and tRNA genes

We have physically mapped the loci conferring resistance to antibiotics that inhibit mitochondrial protein synthesis (erythromycin, chloramphenicol and paromomycin) or respiration (oligomycin I and II), as well as the 21s and 14s rRNA and tRNA genes on the restriction map of the mitochondrial genome of the yeast Saccharomyces cerevisiae. The mitochondrial genes were localized by hybridization of labeled RNA probes to restriction fragments of grande (strain MH41-7B) mitochondrial DNA (mtDNA) generated by endonucleases EcoRI, HpaI, BamHI, HindIII, SalI, PstI and HhaI. We have derived the HhaI restriction fragment map of MH41-7B mit DNA, to be added to our previously reported maps for the six other endonucleases. The antibiotic resistance loci (antR) were mapped by hybridization of 3H-cRNA transcribed from single marker petite mtDNA's of low kinetic complexity to grande restriction fragments. We have chosen the single Sal I site as the origin of the circular physical map and have positioned the antibiotic loci as follows: C (99.5-1.Ou)--P (27-36.Ou)--OII (58.3-62u--OI (80-84u)--E (94.4-98.4u). The 21s rRNA is localized at 94.4-99.2u, and the 14s rRNA is positioned between 36.2-39.8u. The two rRNA species are separated by 36% of the genome. Total mitochondrial tRNA labeled with 125I hybridized primarily to two regions of the genome, at 99.5-11.5u and 34-44u. A third region of hybridization was occasionally detected at 70--76u, which probably corresponds to seryl and glutamyl tRNA genes, previously located to this region by petite deletion mapping.

Study of yeast mitochondrial tRNAs by two-dimensional polyacrylamide gel electrophoresis: characterization of isoaccepting species and search for imported cytoplasmic tRNAs

By two-dimensional polyacrylamide gel electrophoresis, yeast mitochondrial tRNA is fractionated into 27 major species. All but 6 of them migrate distinctly from cytoplasmic tRNAs. Migration of mitochondrial DNA-coded mitochondrial tRNAs shows the occurence of only one cytoplasmic tRNA in mitochondria. Several mitochondrial tRNA spots are identified on the electrophoregrams, some of them show isoaccepting species (Val, Ser, Met, Leu). It is suggested that there are sufficient mitochondrial tRNA genes on yeast mitochondrial DNA to allow mitochondrial protein biosynthesis by the mitochondrial tRNAs alone. Guanosine + Cytidine content and rate base composition are reported for some individual species. Mitochondrial tRNAPhe lacks Ribothymidine.

Fine structure physical mapping of 4S RNA genes on mitochondrial DNA of Saccharomyces cerevisiae

We have localized the genes for mitochondrial 4S RNA on the physical map of the mtDNA of several Saccharomyces cerevisiae strains by hybridization of iodinated 4S RNA to the restriction fragments obtained with endonucleases HindII + III, EcoRI and HapII. The data indicate that 5-8 of the 4S RNA genes are dispersed over a large area of the genome whereas the rest (about 18 genes) is located within an area of about 9000 bp in length (about 18 genes) is located within an area of about 9000 bp in length (about 12% of the genome) between the markers for chloramphenicol and paromomycin resistance (RIB 1 and PAR 1 loci). Within this region a cluster is present of 5 genes on a DNA fragment of 460 bp.

Synthesis of cytochrome c oxidase polypeptides in an Escherichia coli cell-free system directed by Saccharomyces cerevisiae mitochondrial DNA

Using purified yeast mitochondrial DNA as a template for E. coli RNA polymerase (holoenzyme) complementary mitochondrial RNA has been synthesized in vitro. This RNA has been used to direct a low background E. coli S-30 protein-synthesizing system. The synthesis of mitochondrial polypeptides has been detected by using antiserum raised against purified cytochrome c oxidase holoenzyme and shown to be specific for this antigen. The antiserum-antigen complex was dissociated and subject to SDS-polyacrylamide gel electrophoresis and the presence of 3 polypeptides of 39, 31, and 26 X 10(3) daltons molecular weight demonstrated, which correspond to the subunits synthesized by mitochondria in whole cells which are inhibited with cycloheximide.