9513919 Goodenough The long range goal of this project is to analyze the genetic control of sexual differentiation in the unicellular green alga Chlamydomonas reinhardtii. The organism differentiates into 4 distinct cell types during the course of its life cycle and most, if not all, of these programs are governed by its mating-type (mt) locus which exists as a pair of apparent alleles. Cells inheriting the mt+ locus differentiate as plus gametes in response to nitrogen starvation and are capable of mating interactions and zygote formation only with complementary minus alleles. The specific goals of this proposal are: 1. To determine if the gene product of the mid gene is responsible for directing mt- sexual differentiation during gametogenesis and to determine if it acts directly or in concert with other proteins to elicit the transcription of minus- specific structural genes during that period. 2. To define the mechanisms responsible for the movement of the mid gene and about 20 kb of flanking DNA to an autosomal location in a specific strain of C. reinhardtii. Further work will be done to determine the cause for the loss of the element when the autosome is crossed into a plus background. 3. A homologue of the mid gene has been identified in C. incerta, a close relative and experiments will be done to determine similarities or differences in chromosomal location and or configurations. Other more distantly related species will be screened for conservation of the domains of the mid gene. %%% The mid locus of C. reinhardtii has been characterized as the gene responsible for directing mt- sexual differentiation during gametogenesis will be studied in respect to its function. The effect of chromosomal position of the gene will also be studied by comparison with a closely related species of Chlamydomonas where the gene is located on an non-sex chromosome. The level of conservation of the gene will be determined by screening of more distantly related species. These studies should enhance o ur understanding of how sexual differentiation is determined in an important representative of the "early" eukaryotes. ***
