Analysis of divergence of Alphitobius diaperinus satellite DNA--roles of recombination, replication slippage and gene conversion.

Satellite DNA is highly abundant in Alphitobius diaperinus (Tenebrionidae, Coleoptera), comprising 25% of the total genomic DNA. Sequence analysis reveals an average GC content of 50.8% and the presence of three different groups of satellite monomer variants, tH1, tH2 and tH3 with corresponding lengths of 123, 128 and 126 bp. Their mutual homologies range between 65 and 81%. Sequence comparison shows that the monomer variant tH2 has been formed by a recombination process between tH1 and tH3, which have a low average homology of only 65.15%. The longest stretch of 100% homology between the recombining units is 17 bp and is located 3' to the predicted recombination site. There is also an indication from sequence analysis that replication slippage and gene conversion play a part in the formation of satellite units and contribute to their divergence. The tH1, tH2 and tH3 monomer variants are organized in higher order repeating structures: a dimer, composed of tH1 and tH3, and a trimer containing tH1, tH2 and tH3 in series. The dimeric and trimeric repeat units furthermore create three higher order satellite subfamilies. Two of them contain either tandemly arranged dimers or trimers, while the third one is composed of both types of repeats, mutually interspersed.