High Frequency Intragenic Recombination During Macronuclear Development in Tetrahymena thermophila Restores the Wild-type SerH1 Gene

Corresponding author: F. P. Doerder, Department of Biology, Cleveland State University, 1983 E 24th St., Cleveland, OH 44115, doerder{at}biology.csuohio.edu (E-mail).

Communicating editor: S. L. ALLEN

Macronuclear development in ciliates is characterized by extensive rearrangement of genetic material, including sequence elimination, chromosome fragmentation and telomere addition. Intragenic recombination is a relatively rare, but evolutionarily important phenomenon occurring in mitosis and meiosis in a wide variety of organisms. Here, we show that high frequency intragenic recombination, on the order of 30%, occurs in the developing amitotic macronucleus of the ciliate Tetrahymena thermophila. Such recombination, occurring between two nonsense transition mutations separated by 726 nucleotides, reproducibly restores wild-type expression of the SerH1 surface protein gene, thus mimicking complementation in trans heterozygotes. Recombination must be considered a potentially important aspect of macronuclear development, producing gene combinations not present in the germinal micronucleus.

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