THE NEUROSPORA AAB-1 GENE ENCODES A CCAAT BINDING-PROTEIN HOMOLOGOUS TO YEAST HAP5

The expression of the am (glutamate dehydrogenase) gene is dependent u pon two upstream activating sequences, designated URSam alpha and URSa m beta. A heteromeric nuclear protein Am Alpha Binding protein (AAB) b inds specifically to a CCAAT box within the URSam alpha element. AAB a ppears to be composed of three components. We used polyclonal antiseru m raised against the highly purified AAB1 subunit to isolate a partial aab-1 cDNA clone, which was then used to isolate a full-length cDNA a nd a genomic clone. The full-length cDNA has the potential to encode a 272 amino acid protein with a calculated molecular weight of 30 kD. A mino acid sequence obtained by Edman analysis of the AAB1 protein conf irmed that the aab-1 gene had been cloned. AAB-1 shows similarity to t he HAP5 protein of yeast and the CBF-C protein of rat. Each of these p roteins is an essential subunit of their respective heteromeric CCAAT binding proteins. The aab1 gene maps on linkage group III of Neurospor a crassa near the trp-1 locus. Disruption of the aab-1 gene results in pleiotropic effects on growth and development as well as a 50% reduct ion in glutamate dehydrogenase levels. Transformation of the aab-1 dis ruption mutant strain with the cloned genomic copy of the aab-1 gene r escued all of the phenotypic alterations associated with the aab-1 mut ation.