INTERAPTIN, AN ACTIN-BINDING PROTEIN OF THE ALPHA-ACTININ SUPERFAMILYIN DICTYOSTELIUM-DISCOIDEUM, IS DEVELOPMENTALLY AND CAMP-REGULATED AND ASSOCIATES WITH INTRACELLULAR MEMBRANE COMPARTMENTS

In a search for novel members of the a-actinin superfamily, a Dictyost elium discoideum genomic library in yeast artificial chromosomes (YAC) was screened under low stringency conditions using the acting-binding domain of the gelation factor as probe. A new locus was identified an d 8.6 kb of genomic DNA were sequenced that encompassed the whole abpD gene. The DNA sequence predicts a protein, interaptin, with a calcula ted molecular mass of 204,300 D that is constituted by an actin-bindin g domain, a central coiled-coil rod domain and a membrane-associated d omain, In Northern blot analyses a cAMP-stimulated transcript of 5,8 k b is expressed at the stage when cell differentiation occurs. Monoclon al antibodies raised against bacterially expressed interaptin polypept ides recognized a 200-kD developmentally and cAMP-regulated protein an d a 160-kD constitutively expressed protein in Western blots. In multi cellular structures, interaptin appears to be enriched in anterior-lik e cells which sort to the upper and lower cups during culmination. The protein is located at the nuclear envelope and ER. In mutants deficie nt in interaptin development is delayed, but the morphology of the mat ure fruiting bodies appears normal, When starved in suspension abpD(-) cells form EDTA-stable aggregates, which, in contrast to wild type, d issociate, Based on its domains and location, interaptin constitutes a potential link be tween intracellular membrane compartments and the a ctin cytoskeleton.