A method which facilitates the ordering of DNA restriction fragments

A physical map of the Escherichia coli K12 genome

A physical map of a genome is the structure of its DNA. Construction of such a map is a first step in the complete characterization of that DNA. The restriction endonuclease Not I cuts the genome of Escherichia coli K12 into 22 DNA fragments ranging from 20 kilobases (20,000 base pairs) to 1000 kilobases. These can be separated by pulsed field gel electrophoresis. The order of the fragments in the genome was determined from available E. coli genetic information and analysis of partial digest patterns. The resulting ordered set of fragments is a macrorestriction map. This map facilitates genetic and molecular studies on E. coli, and its construction serves as a model for further endeavors on larger genomes.

Characterization of endogenous and exogenous mouse mammary tumor virus proviral DNA with site-specific molecular clones

Restriction fragments of the mouse mammary tumor virus (MMTV) proviral DNA were obtained by molecular cloning procedures. A 4-kilobase fragment delimited by two PstI sites was isolated from unintegrated, linear MMTV DNA and amplified in the pBr322 plasmid vector. EcoRI fragments of proviral DNA, integrated into the genome of a GR mammary tumor cell line, were isolated as lambda recombinant molecules. Five different recombinant phages which contained the 3' region of the MMTV proviral DNA and adjacent host DNA sequences were isolated. Heteroduplex analysis and S1 nuclease digestion suggested that there is no extensive sequence homology in the host DNA flanking the different proviral genes. The cloned DNA was fractionated into site-specific restriction fragments which served as molecular probes in the analysis of the endogenous MMTV proviral copies of C3H, GR, BALB/c, and feral mice. This allowed the correlation of MMTV-specific EcoRI fragments obtained from genomic DNA of these strains with the 5' and 3' ends of the proviral gene. Restriction fragments of two clones which contained the proviral sequences adjacent to the flanking host DNA as well as 1 to 2 kilobases of host DNA were used as hybridization probes, and the results allow the following conclusions: the proviral DNA of both clones contains nucleotide sequences complementary to the 5' and 3' ends of proviral DNA; and the host DNA flanking one clone belongs to the unique class of genomic DNA, whereas the DNA flanking the second clone is reiterated at least 15 times within the mouse genome.

Restriction cleavage maps of coliphages 186 and P2

The restriction enzymes BamHI, Bg/II, EcoRI, HindIII, PstI, XbaI and XhoI have been used to cleave DNA isolated from the related coliphages P2 and 186 for analysis on 1% agarose gels. Three approaches were used to map the sites of cleavage: a) analysis dependent upon the existence of cohesive termini and availability of viable P2-186 hybrids; b) analysis of double digests and redigests of isolated fragments with a second enzyme and c) analysis of partial digests by transfer to nitrocellulose and hybridization with a single fragment. This last approach and the results obtained from it are detailed in a separate paper (Saint and Egan, 1979). The number of sites of each enzyme are as follows: a) 186, BamHI-7, Bg/II-1, EcoRI-3, HindIII-2, PstI-22, XbaI-0 and Xho-I-1; b) P2, BamHI-3, Bg/II-2, EcoRI-3, HindIII-0, PstI-O, XbaI-1 and XhoI-O. All of these sites have been mapped with the exception of PstI for 186, where only the five sites in the right 35% (the control region) have been mapped.