Structure and function of an AT-rich, interspersed repetitive sequence from Chironomus thummi: solenoidal DNA, 142 bp palindrome-frame and homologies with the sequence for site-specific recombination of bacterial transposons.

Chironomus thummi thummi contains a repetitive AT-rich 118 bp sequence mainly in the centromere regions and elsewhere in the genome (1). A large cluster of repeats is regularly present in the non-transcribed spacer of rDNA. Dimers and multimers of the repeat migrate slower in small pore gels than would be expected from their size. The results indicate a solenoidal structure with a coil girth of appr. 350 bp. This structure is most probably due to a highly periodic positioning of di-nucleotides of the type purine - purine or pyrimidine-pyrimidine with distances of appr. 10 bases. In a cluster of 118 bp repeats, regions of dyad-symmetry are positioned such that a 142 +/- 2 bp palindrome-frame is generated. Evidence is presented favouring the assumption that the repeat functions primarily in sister chromatid exchange.