Molecular mechanisms of macronuclear differentiation during late stages of conjugation in the ciliated protozoan Tetrahymena

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To investigate the molecular mechanisms of gene rearrangement during macro- nuclear differentiation, we have cloned and sequenced a Tetrahymena intermediate filament protein (49K protein) gene from a Tetrahymend thermophila macronuclear cDNA library using synthetic oligonucleotides as probes. The 49K protein showed an immunofluorescence localizations suggesting its involvement in the oral morphogenesis preceding binary fission and in nuclear events during fertilization, such as the selection of one of the four meiotic products, formation of the gametic pronuclei, gametic pronuclear transfer, and zygote formation. We have now found that the primary structure of 49K protein not only exhibits homology with those of mammalian vimentin and desmin but also shares 51.5% sequence identity with porcine heart citrate synthase. Furthermore, we demonstrate that 49K protein actually possesses citrate synthase activity, which indicates that 49K protein has dual functions as both a cytoskeletal protein and a respiratory enzyme. On the other hand, we succeeded in making a micronuclear genomic DNA library. Now we are cloning the 49K protein gene from the micronuclear genomic DNA library using 49K protein cDNA as probe.