| Using a human neuroblastoma cDNA library and the yeast two hybrid system to identify novel HASH 1 interacting proteins , we isolated ubiquilin 1 ( DA 41 , hPLIC 1 ) , a gene that contains multiple ubiquitin related domains . ^^^ Ubiquilin 1 is a novel HASH 1 complexing protein that regulates levels of neuronal bHLH transcription factors in human neuroblastoma cells . ^^^ Further analyses showed that ubiquilin 1 interacts not only with HASH 1 , but also with other tissue specific bHLH proteins , including HES 1 . ^^^ Overexpression of ubiquilin 1 led to accumulation of HASH 1 and HES 1 . ^^^ Moreover , ubiquilin 1 was translocated from the cytoplasm to the nucleus upon co expression with HASH 1 . ^^^ |