Centromere 3 specific tandem repeat from Chironomus pallidivittatus

A 155-bp tandem repeat was previously reported to be present in all centrom eric regions of the dipteran Chironomus pallidivittatus. We have now isolat ed a second centromere specific tandem repeat, 375 bp long. Two blocks were found of the new unit, differing in size, probably representing allelic fo rms. The repeat is present only in chromosome 3, bordering 155-bp repeat ar rays. There are about 100 repeats per genome, compared to 1300 units for th e 155-bp repeat. The two units contain an identical 9-bp sequence which can form target-site duplications flanking a short mobile element, Cp1. An inv ersion within the tandem array was isolated, the breakpoint of which is wit hin the 9-bp target sequence. Another short shared motif, IO-bp long, is al so present at the insertion site for a mobile element. The two repeat units are similar in having long regions with more than 80% AT and an overall hi gh AT content.