engleski

Long inversely oriented subunits form a complex monomer of Tribolium brevicornis satellite DNA

Highly abundant satellite DNA named TBREV is detected and characterized in the beetle Tribolium brevicornis (Insecta: Coleoptera). An outstanding peculiarity of TBREV satellite monomer is its complex structure based on the two ∼ 470 bp long subunits, inversely oriented within a 1061 bp long monomer sequence. Proposed evolutionary history demonstrates a clear trend towards increased complexity and length of TBREV satellite monomer. This tendency has been observed on three levels: first as direct and inverted duplications of short sequence motifs, then by inverse duplication of ∼ 470 bp sequence segment, and finally by spread of inversely duplicated elements in a higher-order register and formation of extant monomers. Inversely oriented subunits share similarity of 82%, and have high capacity to form thermodynamically stable dyad structure that is, to our knowledge, the longest ever described in any satellite monomer. Analysis of divergences between inversely oriented subunits shows a tendency to further reduction in similarity between them. Except in its centromeric localization, TBREV satellite does not show similarity to other known Tribolium satellites, either in nucleotide sequence, or in monomer length and complexity. However, TBREV shares common features of other Tribolium satellites that might be under functional constraints: non-constant rate of evolution along the monomer sequence, short inverted repeats in the vicinity of an A+T tract, nonrandom distribution of A or T ≥ 3 tracts and CENP-B box-like motifs. Although long inverted subunits might reinforce structural characteristics of the satellite monomer, their nucleotide sequence does not seem to be under constraints in order to preserve the dyad structure.

inverted repeats; higher-order register; heterochromatin; gene conversion; concerted evolution; Coleoptera

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