GAS41, a highly conserved protein in eukaryotic nuclei, binds to NuMA

The yeast two-hybrid system was used to identify binding partners of NuMA, a component of the nuclear matrix in interphase cells. By using the C-termi nal half of NuMA as bait, a human cDNA sequence coding for a 223-amino acid protein with a non-helical N-terminal domain and a C-terminal a-helical po rtion was identified and fully sequenced. It was identical to GAS41, a sequ ence amplified in human gliomas, The sequence of the homologous Drosophila protein was established, and the alignment for GAS41 from nine different sp ecies showed that GAS41 is a general eukaryotic protein found in species as diverse as Arabidopsis, Drosophila, Caenorhabditis elegans, yeast, and man . Northern blot analysis showed a single transcript in eight human tissues. A polyclonal antibody to GAS41 showed a dotted staining pattern in interph ase nuclei and a uniform distribution in mitotic cells. A GFP-GAS41 fusion protein displayed equivalent patterns. In vitro GAS41 bound to the C-termin al part of the rod region of NuMA, as shown by dot overlay and by surface p lasmon resonance measurements. The K-d of the complex was 2 x 10(-7) M. GAS 41 is related to the AF-9 and ENL proteins, which are putative transcriptio n factors found as fusion proteins in some acute leukemias. The NuMA/GAS41 interaction may provide a link between nuclear structure and gene expressio n.