Nonrandom Localization of DNA Sequences in the Crescent Micronucleus of \u3cem\u3eTetrahymena\u3c/em\u3e

The premeiotic micronucleus of Tetrahymena thermophila elongates parallel to the long axis of the cell. In fixed cells one end of this crescent micronucleus appears thicker than the other, and either end may be oriented toward the anterior of the cell. Three families of repeated DNA sequences have been localized in the crescent micronucleus by in situ hybridization. Two micronucleus-specific sequences hybridize all along the crescent, but preferentially toward the ends. A macronucleus-retained sequence hybridizes preferentially to the half of the micronucleus at the thick end. Thus the arrangement of DNA sequences in the crescent micronucleus is nonrandom