Centromere 3 specific tandem repeat from Chironomus pallidivittatus.

A 155-bp tandem repeat was previously reported to be present in all centromeric regions of the dipteran Chironomus pallidivittatus. We have now isolated a second centromere specific tandem repeat, 375 bp long. Two blocks were found of the new unit, differing in size, probably representing allelic forms. The repeat is present only in chromosome 3, bordering 155-bp repeat arrays. There are about 100 repeats per genome, compared to 1300 units for the 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 inversion within the tandem array was isolated, the breakpoint of which is within the 9-bp target sequence. Another short shared motif, 10-bp long, is also 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 high AT content.