Genetics, Vol 138, 297-301, Copyright © 1994

INVESTIGATIONS

A Temperature-Sensitive Mutation of the Temperature-Regulated SerH3 i-Antigen Gene of Tetrahymena thermophila: Implications for Regulation of Mutual Exclusion

G. L. LaCrosse and F. P. Doerder
Department of Biology, Cleveland State University, Cleveland, Ohio 44115

The Ser genes of Tetrahymena thermophila specify alternative forms of a major cell surface glycoprotein, the immobilization or i-antigen (i-ag). Regulation of i-ag expression assures that at least one i-ag gene is expressed at all times. To learn more about the regulatory system and the possible role of i-ag itself, we studied SerH3-ts1, a temperature-sensitive allele of the temperature-regulated SerH3 gene normally expressed from 20-36{deg}. In homozygotes grown at the nonpermissive temperature (>32{deg}), H3 is not present on the cell surface, but the gene continues to be transcribed until its 36{deg} cutoff. H3 formed at the permissive temperature is stable at nonpermissive temperatures, indicating that SerH3-ts1 is temperature-sensitive for synthesis rather than function. At nonpermissive temperatures, the S i-ag is expressed in place of H3. This result suggests that normal H protein may play a role in regulating S expression. SerH3-ts1 was isolated following mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Sequencing of SerH3-ts1 revealed a single A -> G transition at nucleotide 473, resulting in the substitution of glycine for aspartate. The affected residue is conserved in the internal repeats comprising the H protein, and the charge difference correlates with changes in electrophoretic mobility of the H3 protein.

This article has been cited by other articles:

				J. C. Deak and F. P. Doerder High Frequency Intragenic Recombination During Macronuclear Development in Tetrahymena thermophila Restores the Wild-type SerH1 Gene Genetics, March 1, 1998; 148(3): 1109 - 1115. [Abstract] [Full Text] [PDF]