Selective amplification of variants of a complex repeating unit in DNA of a crustacean.

The nucleotide sequence of the repeating unit of a fraction of the highly repetitive DNA of the red crab, Geryon quinquedens, is reported. Treatment of total DNA with HindIII nuclease produced an 81-base-pair monomer and multimers to the size of an octamer. Several of the multimers contained large amounts of fragments of variant sequences, which cannot easily be explained by random mutation alone. That the alterations were not random was corroborated by divergence measurements made on the distribution of Hha I nuclease sites within several multimers. The analyses showed that a fraction of each of them is characterized by 4% divergence, while the amounts of dimer, tetramer, and octamer suggest that they have undergone 2-4 times more divergence than that. These results, coupled with the data on sequence variants that are more prevalent in the dimer, indicate that amplification of divergent repeating units could easily explain enhanced amounts of selected multimers.