In July of 2011, Dr. Zullo joined NIBIB as Program Director of the Gene and Drug Delivery Portfolio for the Division of Discovery Science and Technology. He currently serves as the NIBIB Inclusion Management Officer and is on the Program Evaluation team in OPESP.

Early in his career, after a postdoctoral fellowship at Yale School of Medicine, Dr. Zullo joined the Laboratory of Biochemical Genetics at National Institute of Mental Health in 1991, where he genetically engineered the first mammalian (Chinese Hamster Ovary) cell line with a functional mitochondrial DNA-encoded gene stably integrated into the nuclear genome (termed allotopic expression). Dr. Zullo also assembled an intramural/extramural team that first demonstrated protease inhibitors (PIs) designed to block the HIV protease could also block the mitochondrial processing protease (MPP). This mechanism might contribute to the lipodystrophy syndromes that first surfaced when PIs were combined with nucleoside analogues (which also affect mitochondria) in highly active antiretroviral therapy (HAART).

Dr. Zullo has coordinated the NIH Mitochondria Interest Group (MIG) since founding it in 1997. He managed chemistry and life sciences projects for the Advanced Technology Program at the National Institute of Standards and Technology from 2000 until 2004. Starting in 2004, he managed the new Gene & Drug Delivery (GDD) Systems Study Section as Scientific Review Officer at the Center of Scientific Review.  He then managed the Biomaterials and Biointerfaces (BMBI) Study section from 2009 until he moved to NIBIB.