CENTROMERIC HETEROCHROMATIN AND SATELLITE DNA IN THE CHIRONOMUS-PLUMOSUS SPECIES GROUP

Species of the Chironomus plumosus group display significant differenc es in their amount of centromeric heterochromatin. A tandem-repetitive satellite-like DNA has been isolated from C, plumosus. This DNA accou nts for a major part of the centromeric heterochromatin. The DNA eleme nt has a Sau3AI restriction site (''Sau elements'') and a monomer leng th of 165 or 166 bp. It is A-T rich (73%) and reveals a moderate DNA c urvature, as shown by gel migration and computer analysis. The chromos omal localization and genomic organization of Sau elements were studie d in 24 Chironomus species by in situ hybridization and (or) Southern analysis. The DNA is predominantly located in the centromeric regions of nine species, six from the plumosus group and three others. In some cases, inter- and intraspecific differences in the size of the centro meric heterochromatin seem to correlate with the strength of Sau eleme nt hybridization signals. Few species contain Sau repeats outside of t he centromeres (C. borokensis, C. plumosus). Additionally, Sau element s are revealed to be present in ectopic threads between centromeres, a nd in B chromosomes found in C. borokensis and C. annularius.