The Bag320 satellite DNA (satDNA) family was studied in seven populations of the stick insects Bacillus atticus (parthenogenetic, unisexual) and Bacillus grandii (bisexual). It was characterized as widespread in all zymoraces of B. atticus and in all subspecies of B. grandii. The copy number of this satellite is higher in the bisexual B. grandii (15%-20% of the genome) than in the parthenogenetic B. atticus (2%-5% of the genome). The nucleotide sequences of 12 Bag320 clones from B. atticus and 17 from B. grandii differed at 13 characteristic positions by fixed nucleotide substitutions. Thus, nucleotide sequences from both species cluster conspecifically in phylogenetic dendrograms. The nucleotide sequences derived from B. grandii grandii could be clearly discriminated from those of B. grandii benazzii and B. grandii maretimi on the basis of 25 variable sites, although all taxa come from Sicily. In contrast, the Bag320 sequences from B. atticus could not be discriminated accordingly, although they derive from geographically quite distant populations of its three zymoraces (the Italian and Greek B. atticus atticus, the Greek and Turkish B. atticus carius, and the Cyprian B. atticus cyprius). The different rate of evolutionary turnover of the Bag320 satDNA in both species can be related to their different modes of reproduction. This indicates that meiosis and chromosome segregation affect processes in satDNA diversification.

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The Bag320 satellite DNA family in Bacillus stick insects (Phasmatodea): different rates of molecular evolution of highly repetitive DNA in bisexual and parthenogenic taxa.

Cloning and characterization of a highly conserved satellite DNA sequence specific for the phytoparasitic nematode Bursaphelenchus xylophilus

Characterization of a complex satellite DNA in the mollusc Donax trunculus: Analysis of sequence variations and divergence

Characterization of CARE-1: Candida albicans repetitive element-1.

We report the coiled-coil structure of DNA, which is generated by the dodecanucleotide d(ATATATATATAT). The structure has been determined by single-crystal x-ray crystallography. The molecules form duplexes with single-stranded overhangs, which associate with neighbor molecules and give rise to infinite double helices in a coiled-coil conformation, with staggered nicks in both strands. The coiled coils have six dodecamer duplexes per turn. Despite the presence of nicks, the structure is very rigid. Statistical disorder is present, which gives rise to continuous scattering along the layer lines. This observation can be interpreted by the classical theory of coiled coils developed for proteins, which we apply here to a DNA structure. A clear splitting of the original layer lines of the DNA double helix is detected. The structure we have found adds a previously unrecognized element to the architectures that can be built from DNA oligonucleotides. Any duplex with complementary single-strand overhangs should be expected to give rise to regular coiled-coil structures.

https://www.pnas.org/content/pnas/102/10/3663.full.pdf

Ferran Azorin

Papers

Detection and molecular cloning of highly repeated DNA in the sea cucumber sperm.