Left/right asymmetrically expressed genes permit an animal to perform distinct tasks with the right vs. left side of its brain. Once established during development, lateralized gene expression patterns need to be maintained during the life of the animal. We show here that a histone modifying complex, composed of the LSY-12 MYST-type histone acetyltransferase, the ING-family PHD domain protein LSY-13, and PHD/bromodomain protein LIN-49, is required to first initiate and then actively maintain lateralized gene expression in the gustatory system of the nematode Caenorhabditis elegans. Similar defects are observed upon postembryonic removal of two C2H2 zinc finger transcription factors, die-1 and che-1, demonstrating that a combination of transcription factors, which recognize DNA in a sequence-specific manner, and a histone modifying enzyme complex are responsible for inducing and maintaining neuronal laterality.