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At least 37 records · Page 2Linked to original sources
PubMed1976

On the mechanism of genetic recombination: electron microscopic observation of recombination intermediates.

This paper deals with the nature of recombination intermediates. Using the electron microscope to study the DNA of the plasmid colicin E1, we have observed more than 800 molecules that appear to represent intermediates in the process of recombination. Specifically, after isolating colicin DNA and linearizing it with the restriction enzyme EcoRI, we find crossed molecules with twice the normal colicin DNA content. These forms consist of two genome-length elements held together at a region of DNA homology. The molecules can be recovered from wild type and Rec B-C host cells but are not present among the colicin DNA forms isolated from recombination-deficient Rec A cells. We have termed the experimentally observed molecules "chi forms" and believe that they represent the recombination intermediate of the Holliday model.

Colicins↗
PubMed1977

On the mechanism of genetic recombination: the maturation of recombination intermediates.

DNA molecules of the plasmid ColEl are normally recovered from wild-type cells as a set of monomer- and multimer-size rings. The data of this paper show that the multimer-size species are a product of genetic recombination. Multimer rings do not arise after transfection of purified monomers into bacterial host cells lacking a functional recA recombination system. Analogously, purified dimers, trimers, and tetramers, transfected into recA- cells, can replicate, but are constrained to remain in those conformations. Only upon transfection into rec+ cells can they regenerate the full spectrum of monomer- and multimer-size species. In this paper we trace the flow of genetic information from the monomer to the multimer state and back again under the guidance of the recA recombination system. The formation of multimer-size DNA rings is discussed as a natural consequence of the maturation of a Holliday recombination intermediate formed between two monomer plasmid genomes.

Chromosomes↗
PubMed1976

Age trends in human chiasma frequencies and recombination fractions. II. Method for analyzing recombination fractions and applications to the ABO:nail-patella linkage.

A new method is presented for studying the relationship between human recombination fractions and parental age at the time of conception. Assuming the sex specific recombination fraction to be a linear function of age, a feasible computer algorithm is described whereby the likelihood of multigenerational families can be calculated. Using this method and the likelihood ratio test, it is found that for the ABO:nail-patella linkage age (P= .17)is more significant than sex (p= .23) in its effect on the recombination fraction. The age effect, if it is real, appears to be limited to males: the paternal recombination fraction decreases by .0062(+/- .0036) per year.

ABO Blood-Group System↗
PubMed1976

Role of the bacterial and phage recombination systems and of DNA replication in genetic recombination of UV-irradiated phage Lambda.

In this paper are studied in E. coli K12 the influence of the bacterial Rec and phage mu Red recombination systems on the rescue of the O plus gene from the prophage by a superinfecting O minus phage, UV irradiated or not. In the absence of UV irradiation the Red system produces more recombinants than does the Rec system, and its action requires DNA replication. The presence of UV lesions in the mu DNA facilitates the action of the Rec system, which is more efficient in this instance than the Red system and can act in the absence of DNA replication. In all cases, there is a cooperation between the two generalized recombination systems.

Coliphages↗
PubMed1979

Genetic recombination in Rous sarcoma virus: the genesis of recombinants and lack of evidence for linkage between pol, env and src genes in three factor crosses.

Three factor crosses were performed between Rouse sarcoma virus mutants with temperature-sensitive markers in the pol and src genes and host range markers in the env gene. A number of recombinant viruses appeared to segregate from virus particles which were heterozygous for all three genes under study. The frequency of various recombinant genotypes in the progeny was consistent with there being no greater linkage between the neighbouring gene pairs of pol and env and env and src than between the more distant pol and src. The significance of these results to proposed mechanisms of avian retrovirus recombination is discussed.

Animals↗
PubMed1975

Site specific recA--independent recombination between bacterial plasmids: involvement of palindromes at the recombinational loci.

A recA-independent recombinational event is described which results in insertion of an entire plasmid genome at a unique site of another plasmid, and coincident excision of a precisely defined DNA segment originally present at the point of the insertion. The resulting recombinant molecules subsequently can undergo site-specific translocation of their component segments or inversion of their original DNA sequence orientation. The events observed entail nonreciprocal exchange of genetic material, and involve a discrete nucleotide sequences that is duplicated in rotationally symmetrical reverse orientation on plasmid DNA (i.e., inverted repeat; palindrome).

Base Sequence↗
PubMed1975

Electron microscopy of meiosis in Drosophila melanogaster females: II. The recombination nodule--a recombination-associated structure at pachytene?

The recombination nodule is a transient structure present during pachytene in intimate association with the synaptonemal complex. The total numbers of these structures per nucleus and their locations along the bivalents correspond to the total numbers and distributions of genetic exchanges. It is suggested that this structure may be involved in the recombination process.

Animals↗
PubMed1977

[Formation of recombinants of F' plasmids in recombination-defective E. coli cells and their properties].

As a result of mating of cells carrying plasmid F' lac with cells carrying plasmid F'his merodiploids carrying plasmid complex F'lacF'his were isolated. The plasmid genes of the isolated merodiploids are donated together into the recipient cells and are eliminated jointly from host-cells both spontaneously and by acridine orange. As the formation of the plasmid complex took place in E. coli cells carrying mutation in rec A gene the recombination of plasmids F' is supposed to take place in the absence of the product of gene rec. A.

Escherichia coli↗
PubMed1976

[Mechanism of genetic recombination during bacterial recombination. VI. Single-stranded conjugation].

The mutation BT43 in the dnaB gene inhibits conjugational DNA synthesis in the recipient cell at 42 degrees C. Since only one DNA strand is transferred from the donor to the recipient in these conditions, this single strand is integrated into the recipient chromosone. This is characterized by a high increase of recombination frequency per length unit, an effect well known in the case of transformation. This peculiar genetic process is proposed to be called "single stranded conjugation". It is more efficient in recipient cells recB-recC-sbcB-lacking two main degrading enzymes, exonucleases I and V. The proof of single strandedness was given by means of clonal analysis in a special experiment. The transfer of the selected marker into the thermosensitive recipient took place at 37 degrees C and the transfer of the non-selected marker -- at 42 degrees C. Thhe progeny of one merozygote must be mixed i.e. consist of cells with both alleles of the non-selected marker. This was confirmed by experimental data.

Conjugation, Genetic↗