Mating type in Chlamydomonas is specified by mid, the minus-dominance gene.
Diploid cells of Chlamydomonas reinhardtii that are heterozygous at the mating-type locus (mt+/mt-) differentiate as minus gametes, a phenomenon known as minus dominance. We report the cloning and characterization of a gene that is necessary and sufficient to exert this minus dominance over the plus differentiation program. The gene, called mid, is located in the rearranged (R) domain of the mt- locus, and has duplicated and transposed to an autosome in a laboratory strain. The imp11 mt- mutant, which differentiates as a fusion-incompetent plus gamete, carries a point mutation in mid. Like the fus1 gene in the mt+ locus, mid displays low codon bias compared with other nuclear genes. The mid sequence carries a putative leucine zipper motif, suggesting that it functions as a transcription factor to switch on the minus program and switch off the plus program of gametic differentiation. This is the first sex-determination gene to be characterized in a green organism.
Ferris
P J
PJ
Department of Biology, Washington University, St. Louis, Missouri 63130, USA. ferris@wustlb.wustl.edu
Goodenough
U W
UW
D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000235:genetics*; D002874:Chromosome Mapping; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D005799:Genes, Dominant; D008969:Molecular Sequence Data
D001426:Bacterial Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C107853:Mid protein, Chlamydomonas reinhardtii