Higher-order repeats in the satellite DNA of the cave beetle Pholeuon proserpinae glaciale (Coleoptera: Cholevidae).

The present study characterizes the satellite DNA of the cave beetle Pholeuon proserpinae glaciale which represent about 3-5 % of its genome, and which is composed of monomers of 266 bp and 70.5 % A-T. Concerted evolution seems to act on a higher-order repeat, a dimer, composed of two types of 266-bp monomers that differ in three diagnostic sites. These dimers show a striking nucleotide identity (98.7 % similarity) suggesting strong homogenization processes. The presence of particular mutations shared by several dimers represents an early expansion of these types of repeats as proposed by the molecular drive model. Moreover, evidence of gene conversion tracts in P. proserpinae glaciale, which also could be the result of unequal sister chromatid exchange, would suggest that recombination is involved in the homogenization of stDNA sequences. The presence of a 17-bp-motif repeated six times, along another one of 31-bp repeated twice which also have embedded one 17-bp-motif, suggest that monomers have originated from those basic motifs.