NON-MENDELIAN INHERITANCE OF MACRONOCLEAR TRAITS

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The broad aim of this proposal is to elucidate the molecular details of an unusual type of non-Mendelian inheritance in Paramecium tetraurelia. We will combine molecular biology and genetics to study a mutant cell line (d48) that contains a complete copy of the A type variable surface antigen gene in the micronucleus but not in the macronucleus. Wild type cytoplasm allows the incorporation of these sequences into the macronucleus, but in d48 cytoplasm the chromosome is broken incorrectly and the A gene is deleted. Recent experiments have shown that macronuclear transformation of d48 with a recombinant clone containing the A antigen gene (pSA14SB) leads to the correct processing of the micronuclear A gene sequences during the formation of the next macronucleus (K. Aufderheide, personal communication). By microinjecting specific fragments of pSA14SB into the d48 macronucleus we will define the DNA sequences necessary for the correct processing of the A gene. Further experiments will be performed to determine if RNA products from these sequences are important for their function. Micronuclear DNA from the d48 and wild type cell lines will be isolated and used to compare the organization of the micronuclear sequences surrounding the chromosome breakage sites. Additional non-Mendelian mutants have recently been isolated that affect expression of the B surface antigen gene (J. Preer, personal communication). We will clone the B gene and determine if similar molecular mechanisms are involved in these mutations. We believe this research will advance the understanding of developmentally controlled DNA rearrangements in eukaryotes, and perhaps reveal novel aspects of nucleic acid processing.