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PubMed1981

Elimination of mitochondrial elements and improved viability in hybrid cells.

Experiments were carried out to determine whether the mitochondria-specific dye rhodamine-6G (R6G) can affect transmission of cytoplasmic determinants in mammalian cells. When one parental cell type was treated with R6G prior to fusion with an untreated partner, the subsequent hybridization frequencies in both intra- and interspecific crosses were not adversely affected, even though R6G was extremely toxic to the parental cells. In addition, cells lethally treated with R6G could be rescued by fusion with cytoplasm alone from untreated cells. When chloramphenicol (CAP) resistant cells were used as the R6G-treated parent, the expression of CAP resistance in hybrids and cybrids was greatly reduced. Thus R6G can be used to control the input of cytoplasmic determinants into fused cells. In the interspecific (Chinese hamster x mouse) crosses, it was also seen that the majority of hybrids which had not been R6G pretreated grew poorly or degenerated after a short time. In contrast, nearly all hybrids in crosses where the hamster parent was R6G pretreated grew vigorously. The concomitant elimination of inviability and loss of mitochondrial determinants in R6G-pretreated hybrids suggests that interactions involving mitochondrial gene products or components can influence growth characteristics in interspecific somatic cell hybrids.

Animals↗
PubMed1977

Determinant for multiple drug resistance possessing features of a mitochondrial episome in Saccharomyces cerevisiae.

A mutation for multiple resistance to tetracycline, cycloheximide and oligomycin appears to be followed by reconstruction of the mitochondrial genome resulting in the formation of independent nucleotide sequences that determine different resistant phenotypes. Heterozygotes for the cross resistance factor lack locus T responsible for relation tetracycline which comes from the alpha-parent. The nuclear recessive gene-suppresor i induces deletion of the whole determinant for multiple resistance. The loss of mt-DNA on ethidium bromide treatment does not lead to the loss of this determinant which remains in the cells either in an active or in a passive state.

Alleles↗
PubMed1976

Extrachromosomal DNA and RNA-synthesis in oocytes of Creophilus maxillosus (Staphylinidae, Coleoptera, Polyphaga).

It has been found that the transcriptional activity of nuclear extra DNA in Creophilus maxillosus oocytes, as examined by autoradiography, increases parallel with its dispersion during the previtellogenic period of oocyte growth. The RNA, after being synthesized in the greatly enlarged oocyte nucleus, is subsequently transported into the cytoplasm. The oocyte chromosomes form a karyosphere and synthesize the RNA more weakly than other parts of the nucleus, which contain the extra DNA in a highly dispersed condition.

Animals↗
PubMed1986

Mitochondrial DNA evolution in the melanogaster species subgroup of Drosophila.

Detailed restriction maps (40 cleavage sites on average) of mitochondrial DNAs (mtDNAs) from the eight species of the melanogaster species subgroup of Drosophila were established. Comparison of the cleavage sites allowed us to build a phylogenetic tree based on the matrix of nucleotide distances and to select the most parsimonious network. The two methods led to similar results, which were compared with those in the literature obtained from nuclear characters. The three chromosomally homosequential species D. simulans, D. mauritiana, and D. sechellia are mitochondrially very related, but exhibit complex phylogenetic relationships. D. melanogaster is their closest relative, and the four species form a monophyletic group (the D. melanogaster complex), which is confirmed by the shared unusual length of their mt genomes (18-19 kb). The other four species of the subgroup (D. yakuba, D. teissieri, D. erecta, and D. orena) are characterized by a much shorter mt genome (16-16.5 kb). The monophyletic character of the D. yakuba complex, however, is questionable. Two species of this complex, D. yakuba and D. teissieri, are mitochondrially indistinguishable (at the level of our investigation) in spite of their noticeable allozymic and chromosomal divergence. Finally, mtDNA distances were compared with the nuclear-DNA distances thus far established. These sequences seem to evolve at rather similar rates, the mtDNA rate being barely double that of nuclear DNA.

Animals↗
PubMed1977

Excision of a DNA sequence determining kanamycin resistance from a ColE1-Km recombinant plasmid.

A 4.8 X 10(6) dalton ECoRI-generated fragment of the R-factor R6-5 carrying the gene for kanamycin resistance (Km) was joined in vitro to ECoRI-treated ColE1 plasmid DNA. Transformation of E. coli with the ColE1-Km recombinant plasmid yielded clones, which were immune to colicin E1, resistant to kanamycin and failed to produce colicin E1. During multiplication of this recombinant plasmid in the presence of chloramphenicol, cells expressed an increased resistance to kanamycin. Transformation studies with the recombinant DNA molecule showed very frequent loss of Km resistance in those cells harbouring a preexisting F'gal plasmid. Since colicin immunity is not affected and the col- phenotype is still present, one has to test for a remaining DNA sequence further existing in ColE1 DNA by cleaving the plasmid DNA with the ECoRI restriction endonuclease. The full length of ColE1 DNA (6.2 kb) was restored, which confirmed that no deletion of ColE1 DNA sequences had occured. The remaining DNA sequence was identified as a 2.0 or 2.2 kb segment. On the basis of the length of the excised fragment it is proposed that the insertion sequence ISI and a part of the inverted repeat sequence with corrdinates 21.0 to 22.0 of the R6-5 DNA are recognised by a nucleolytic function.

Colicins↗
PubMed1976

Mutants of the Clo DF13 plasmid in Escherichia coli with a decreased bacteriocinogenic activity.

Three Clo DF13 mutant plasmids (designated as clp03, clp05 and clp21) that show a decreased cloacin activity were isolated. The decreased cloacin activity was not due to a reduced number of Clo DF13 copies per cell. The cloacins produced by the clp03 and the clp21 mutant plasmids have a strongly decreased killing activity in vivo in comparison with the wild type cloacin and the cloacin of the clp05 mutant plasmid. Furthermore no lacunae could be observed from clp03 or clp21 harbouring strains, while strains harbouring the clp05 plasmid showed a 50-100 times decreased frequency of lacunae. In addition the clp05 mutant showed a decreased rate of RNA synthesis in clp05 harbouring Escherichia coli minicells. No complementation between the three mutant plasmids was observed. We suggest that the clp03 and clp21 mutations are located in the gene coding for the cloacin. Since the cloacin produced by the clp05 mutant plasmid has retained all the known wild type cloacin activities, the reduced inhibition zone in the stab test is probably caused by a mutation affecting the expression of the cloacin gene. The nature of this mutation is discussed.

Bacterial Proteins↗
PubMed1976

Plasmids controlling synthesis of hemolysin in Escherichia coli. II. Polynucleotide sequence relationship among hemolytic plasmids.

Plasmids of three different sizes, designated as plasmid A (mw: 65 X 10(6), plasmid B (mw: 41 X 10(6) and plasmid C (mw: 32 X 10(6) respectively, have been isolated from various hemolytic wild-type strains of E. coli. DNA-DNA hybridization was performed to determine their relationship. The wild-type strain, PM167a, harbours plasmids of all three sizes. Hybridization studies indicate that all three plasmids share extented sequence homologies but that plasmid A is not composed of plasmids B and C. Hybridization between plasmids of the donor strain and those of appropriate transconjugants demonstrates that in some cases plasmids with identical size are not longer completely homologous in their nucleotide sequences. This indicates that despite their defined sizes these plasmids are not stable genetic entities, but rather they undergo frequently recombination and dissociation during conjugation. In one particular transconjugant strain, K12-PM152/1, a plasmid D was found which is a stable recombined molecule of plasmids B and C of the original strain. Plasmids of size B found as the only extrachromosomal elements in a hemolytic wild-type strain (P224) and two transconjugant strains (e.g. K12-CM20 and K12-PM167/1) share extended nucleotide sequence homologies but are not identical. Little sequence homology was observed between two different hemolytic plasmids and the F and the Col Ib plasmids suggesting that the former do not belong to either the F-like or the I-like group of plasmids. Another hemolytic plasmid is F-like based on its sequence homologies with the F factor.

Base Sequence↗
PubMed1976

The maintenance affinities of KLF-1 proximal F merogenotes in Escherichia coli.

In conjugation with donor strains carrying proximal F merogenotes of KLF-1 type about 100-fold lower frequency of Leu+ or Lac+ recombinants was found. The determination of the level of beta-galactosidase synthesis during the initial period of mating indicated that the transfer process of plasmid DNA was not impaired. Among the recombinants selected a large fraction have not expressed the plasmic fertility functions. This phenomenon was found to be replicon specific and was observed only with proximal F merogenotes but not with classical F'lac and F'ORF-1 elements or R1-19 plasmid. The expression of KLF-1 plasmid functions in the cell seems to be affected by a chromosomal gene of the proximal F merogenote closely linked to leu marker.

Ampicillin↗