Judy M. Goddard

Nucleotide Sequence Variants of Rattus norvegicus Mitochondrial DNA

The mitochondrial DNA (mtDNA) molecules of different albino, domesticated rats (Rattus norvegicus) of the SASCO colony are of two kinds (SASCO-1 and SASCO-2) in regard to their sensitivity at certain sites to a number of restriction enzymes. MtDNA molecules from Utah wild R. norvegicus (Wild-UT) have sensitivities to restriction enzymes which differ at some sites from either SASCO-1 or SASCO-2 mtDNA molecules. Four single nucleotide differences were found among the HindIII F fragments (169 nucleotides) of SASCO-1, SASCO-2, and Wild-UT mtDNAs. Arguments are presented in favor of the interpretation that each variant nucleotide is the third nucleotide of the codon containing it, and that none of the four differences would result in a difference in the respective amino acid translated.

STRUCTURE AND REPLICATION OF MITOCHONDRIAL DNA FROM THE GENUS DROSOPHILA

ABSTRACT Mitochondrial DNA (mtDNA) molecules from different species of the melanogaster group of the genus Drosophila differ in size from 15.7 to 19.5 kilobase pairs (kb). These differences appear to be accounted for by differences in size (1.0 to 5.4 kb) of a single adenine and thymine (A+T)-rich region in each molecule. The sizes of the mtDNA molecule of other Drosophila species are within the narrow range 15.7 to 16.8 kb, and contain an A+T-rich region of approximately 1.0 kb. Restriction enzyme mapping results indicate the A+T-rich region of D. melanogaster, D. simulans, D. mauritiana, D. takahashi, and D. virilis to be at homologous positions on the mtDNA molecules. We have studied the various structural forms of partially replicated mtDNA molecules from the above mentioned species, and concluded that in each species most molecules are replicated by a highly asymmetrical mode in which synthesis on one strand can be between 60% and 100% complete before synthesis on the other strand is initiated. Using the A+T-rich regions and EcoRI cleavage sites as markers, we have determined that in all species studied replication of mtDNA molecules is initiated in the A+T-rich region and proceeds unidirectionally around the molecule towards the nearest EcoRI site common to the mtDNAs of all six species. We have found that the A+T-rich regions of the different species have little or no sequence homologies.

Nucleotide Sequences within the A + T-rich Region and the Large-rRNA Gene of Mitochondrial DNA Molecules of Drosophila yakuba

mtDNA molecules of species of the genus Drosophila contain a region that is distinctly rich in adenine and thymine (A + T). In different species of the melanogaster group, the A + T-rich region ranges in size from 1.0 kb to 5.1 kb, whereas in D. virilis and other species it is about 1.1 kb (for references, see Fauron and Wolstenholme 1980a,b). We have shown that in mtDNA molecules of D. melanogaster, D. simulans, D. mauritiana, D. takahashii, D. yakuba, and D. virilis, the A + T-rich regions (5.1, 4.8, 4.6, 2.5, 1.1, and 1.1 kb, respectively) are homologously located. Using heteroduplex analyses, we have demonstrated that extensive divergences of sequences have occurred in A + T-rich regions of mtDNA molecules, both within species as well as between species (Fauron and Wolstenholme 1980a,b). In all six of the species mentioned above, the origin of replication lies within the A + T-rich region; replication is unidirectional around the molecule as a whole and always occurs in the same direction (Goddard and Wolstenholme 1980). The direction of replication in Drosophila mtDNA is toward the adjacently located rRNA genes, which is opposite to the direction of replication in vertebrate mtDNAs (see Wolstenholme et al. 1979). RNA transcripts that map in the A + T-rich region have not been detected, and apart from its inclusion of the replication origin, no other function of this region is known (for discussion and references, see Fauron and Wolstenholme 1980b). We report here the results of sequence studies...

Nucleotide sequence of Rattus norvegiens mitochondrial DNA that includes the genes for tRNAile, tRNAgln and tRNAf-met

The nucleotide sequence of a segment of mtDNA from Rattus norvegicus (rat) which contains the genes for tRNAile, tRNAgln and tRNAf-met has been determined. A detailed comparison has been made between this sequence and the corresponding sequences of mouse, human and bovine mtDNAs with regard to the primary and secondary structure of the tRNA genes, the regions connecting the tRNA genes, and the regions flanking the tRNA genes which code for the carboxyl terminus of URF-1 and the amino terminus of URF-2. No differences were found in the nucleotide sequences of the genes for tRNAile, tRNAgln and tRNAf-met in mtDNAs from three different female lines of rats (SASCO-1, SASCO-2 and Wild-UT) that differ by substitutions of 0.8% to 1.8% of their total nucleotides.

Replication of Drosophila Mitochondrial DNA

Mitochondrial DNA (mtDNA) molecules of Drosophila include a region of exceptionally high adenine + thymine (A+T) content which, though homologously located, varies in size from 1.0 kb to 5.1 kb in different species. In all species examined, replication begins at a unique site within the A+T-rich region and proceeds in the same direction towards the molecule’s ribosomal RNA genes. Most molecules are replicated by a highly asymmetrical mode in which synthesis of one strand can be up to 100% complete before synthesis of the second strand is initiated. In a minority of molecules, a more symmetrical mode of synthesis is employed. Evidence has been obtained that within A+T-rich regions extensive sequence divergences have taken place both between species and within species. The A+T-rich region shares many features with the replication origin-containing region of vertebrate mtDNA molecules, supporting the view that the two regions are derived from a common ancestral sequence.

CeAb1: Abl-related PTK (C. elegans)

The Caenorhabditis elegans abl gene was identified by virtue of its sequence similarity to the mouse c-ab1. The predicted protein product, CeAb1, of the gene contains structural domains that exhibit up to 67% amino acid identity with similar domains in the mouse protein. Subunit of CeAb1 protein comprise 1210 amino acids and molecular weight of 13600. Database accession number of CeAbl is M13235 for EMBL. Sites of interest in protein are Y448, putative autophosphorylation; the N-terminal 7 amino acids are predicted from the genomic sequence only and have not been confirmed by cDNA clones.