GROWTH AND DEVELOPMENTAL FUNCTIONS OF A HUMAN-IMMUNODEFICIENCY-VIRUS TAT-BINDING PROTEIN 26S PROTEASE SUBUNIT HOMOLOG FROM DICTYOSTELIUM-DISCOIDEUM

We have characterized a newly identified gene from Dictyostelium disco ideum, DdTBP alpha, that encodes a member of the family of eukaryotic proteins. These proteins contain a conserved ATPase domain, include su bunits of the 26S protease subunit, and are homologous to the mammalia n human immunodeficiency virus Tat-binding protein TBP1, While informa tion indicates that some family members are involved in the regulation of transcription in mammalian and yeast cells during growth, these pr oteins are also involved in other cellular functions, and nothing is k nown about their possible function in multicellular development, The D ictyostelium DdTBP alpha gene is developmentally regulated, with its e xpression at the highest levels occurring during growth and early deve lopment. The gene is present in two copies in the genome, Disruption o f one copy by homologous recombination leads to aberrant morphogenesis , which lasts from the formation of the first finger until the onset o f culmination, The gene appears to be essential for growth since we we re unable to obtain a complete null phenotype and since expression of an inducible antisense construct in the partial null background result ed in cell death. Expression of the antisense construct during develop ment accentuated the partial null phenotype and also resulted in very abnormal fruiting bodies. Overexpression of DdTBP alpha from its own p romoter leads to very large multinucleated vegetative cells when the c ells are grown in suspension culture. When the cells are plated onto p etri dishes in growth medium, they rapidly split into multiple cells c ontaining one to two nuclei, in a manner similar to that of wild-type cells. Overexpressing cells are significantly delayed in forming a mul ticellular aggregate, but development proceeds normally once the first finger stage is reached. The results indicate that DdTBP alpha plays an important role in regulating both growth and morphogenesis in D. di scoideum.