Sequencing Of DNA Molecules Research Articles

Identification of 16S ribosomal DNA-defined bacterial populations at a shallow submarine hydrothermal vent near Milos Island (Greece).

In a recent publication (S. M. Sievert, T. Brinkhoff, G. Muyzer, W. Ziebis, and J. Kuever, Appl. Environ. Microbiol. 65:3834-3842, 1999) we described spatiotemporal changes in the bacterial community structure at a shallow-water hydrothermal vent in the Aegean Sea near the isle of Milos (Greece). Here we describe identification and phylogenetic analysis of the predominant bacterial populations at the vent site and their distribution at the vent site as determined by sequencing of DNA molecules (bands) excised from denaturing gradient gels. A total of 36 bands could be sequenced, and there were representatives of eight major lineages of the domain Bacteria. Cytophaga-Flavobacterium and Acidobacterium were the most frequently retrieved bacterial groups. Less than 33% of the sequences exhibited 90% or more identity with cultivated organisms. The predominance of putative heterotrophic populations in the sequences retrieved is explained by the input of allochthonous organic matter at the vent site.

Type I restriction systems: sophisticated molecular machines (a legacy of Bertani and Weigle).

Restriction enzymes are well known as reagents widely used by molecular biologists for genetic manipulation and analysis, but these reagents represent only one class (type II) of a wider range of enzymes that recognize specific nucleotide sequences in DNA molecules and detect the provenance of the DNA on the basis of specific modifications to their target sequence. Type I restriction and modification (R-M) systems are complex; a single multifunctional enzyme can respond to the modification state of its target sequence with the alternative activities of modification or restriction. In the absence of DNA modification, a type I R-M enzyme behaves like a molecular motor, translocating vast stretches of DNA towards itself before eventually breaking the DNA molecule. These sophisticated enzymes are the focus of this review, which will emphasize those aspects that give insights into more general problems of molecular and microbial biology. Current molecular experiments explore target recognition, intramolecular communication, and enzyme activities, including DNA translocation. Type I R-M systems are notable for their ability to evolve new specificities, even in laboratory cultures. This observation raises the important question of how bacteria protect their chromosomes from destruction by newly acquired restriction specifities. Recent experiments demonstrate proteolytic mechanisms by which cells avoid DNA breakage by a type I R-M system whenever their chromosomal DNA acquires unmodified target sequences. Finally, the review will reflect the present impact of genomic sequences on a field that has previously derived information almost exclusively from the analysis of bacteria commonly studied in the laboratory.

Biology, boundaries and borders

Towards Justice and Peace is a splendid title for a symposium and book to honour Professor Sunderland. It is also a very difficult title for a biological anthropologist. I make the distinction from social anthropology with some apology. There are of course many subdisciplines and traditions within Anthropology and I most associate Professor Sunderland's support of my university and myself with our attempts to foster cross-disciplinary discussion, towards a “Biosocial Anthropology”, as it were. So, while for specialists in fossilization of bones, sequences of DNA molecules or analysis of urine, the title, Towards Justice and Peace might cause problems, I should like to discuss some biosocial anthropology on an international frontier, which, after centuries of military aggression and defence, is now a peaceful line on a map within the European Community. HMM.

Investigation of the influence of cytosine methylation on DNA flexibility.

To test the influence of pyrimidine methyl groups on DNA flexibility and helix repeat, two sets of 14 mixed sequence DNA molecules, spanning a range of lengths from 158 to 180 base pairs, were cyclized with T4 DNA ligase. The two sets differed only in that the Cyt-5 positions of all cytosines (80-90 cytosine residues per molecule) were fully methylated in the members of one set. Determination of the molar cyclization factors, persistence lengths, helix repeats, and torsional elastic constants revealed no significant differences between the two sets. These results imply that, at least for mixed sequence DNA, the biological consequences of cytosine methylation are likely to derive from either local structural distortions in the helix, which do not propagate as altered twist, or from direct protein-methyl cytosine interactions.

Mechanisms of DNA Reorganization in Bacteria

Publisher Summary This chapter discusses the mechanisms of DNA reorganization in bacteria. Many biochemical systems exist precisely for creating new DNA structures. Nucleotide sequences in DNA molecules constitute one of the main systems for information storage in living cells. As organisms encounter varying external environments and create new internal environments for their cells, they often need to change the stored information. Biochemical components involved in the genetic change include all the activities involved in the creation of a transposable resistance determinant and its transposition to a transmissible plasmid, the activities required for plasmid replication and segregation, and the activities required for conjugal plasmid transfer of specific proteins and cell structural components. Many proteins active on DNA either do not catalyze specific chemical reactions or do not show turnover but rather function in a stoichiometric manner. The absence of turnover facilitates the control of DNA reorganizations because they can be restricted to a few reactions by limiting the amount of the proteins involved. Proteins, which act enzymatically might carry on repeated DNA reorganizations.

Somatic association of telocentric chromosomes carrying homologous centromeres in common wheat

Measurements of distances between telocentric chromosomes, either homologous or representing the opposite arms of a metacentric chromosome (complementary telocentrics), were made at metaphase in root tip cells of common wheat carrying two homologous pairs of complementary telocentrics of chromosome 1 B or 6 B (double ditelosomic 1 B or 6 B). The aim was to elucidate the relative locations of the telocentric chromosomes within the cell. The data obtained strongly suggest that all four telocentrics of chromosome 1 B or 6 B are spacially and simultaneously co-associated. In plants carrying two complementary (6 B (S) and 6 B (L)) and a non-related (5 B (L)) telocentric, only the complementary chromosomes were found to be somatically associated. It is thought, therefore, that the somatic association of chromosomes may involve more than two chromosomes in the same association and, since complementary telocentrics are as much associated as homologous, that the homology between centromeres (probably the only homologous region that exists between complementary telocentrics) is a very important condition for somatic association of chromosomes. The spacial arrangement of chromosomes was studied at anaphase and prophase and the polar orientation of chromosomes at prophase was found to resemble anaphase orientation. This was taken as good evidence for the maintenance of the chromosome arrangement - the Rabl orientation - and of the peripheral location of the centromere and its association with the nuclear membrane. Within this general arrangement homologous telocentric chromosomes were frequently seen to have their centromeres associated or directed towards each other. The role of the centromere in somatic association as a spindle fibre attachment and chromosome binder is discussed. It is suggested that for non-homologous chromosomes to become associated in root tips, the only requirement needed should be the homology of centromeres such as exists between complementary telocentrics, or, as a possible alternative, common repeated sequences of DNA molecules around the centromere region.

Nucleotide sequence analysis of DNA.

There are three major obstacles to the analysis of the nucleotide sequence in a DNA molecule starting from a known location in the DNA molecule. First, it is difficult to obtain large quantities of homogeneous DNA. Second, even the smallest DNA molecules contain several thousand nucleotides which make sequence analysis prohibitive. Third, there are no highly base-specific DNAases available for degrading DNA for sequence analysis. We have overcome some of these obstacles; first, by incorporating highly labelled deoxynucleotides into DNA in vitro, small amounts of material can be used for sequence analysis. Second, the nucleotide sequence of DNA molecules can now be determined from the 5′-terminal. Thus, two dodecanucleotide sequences corresponding to the two cohesive ends of λ DNA have been determined1, and a nona-decanucleotide sequence corresponding to one cohesive end of phage 186 DNA has been completed2. So far, our approach is limited to starting the analysis from the 5′-ends of a DNA molecule. A more general approach is being developed for starting the analysis from other selected parts of a DNA molecule with the use of specifically designed primers.