The Nuclear Factor I (NFI or NF-1) family of site-specific DNA-binding proteins (also known as CTF or AAT box transcription actor) functions both in viral DNA replication and in the regulation of gene expression. The classes of genes whose expression is modulated by NFI include those that are ubiquitously expressed, as well as those that are hormonally, nutritionally, and developmentally regulated. The NFI family is composed of four members in vertebrates (NFI-A, NFI-B, NFI-C and NFI-X). Products of the four NFI genes differ in their abilities to either activate or repress transcription, likely through fundamentally different mechanisms. In addition, NFI proteins have been associated with changes in the growth state of cells and with a number of oncogenic processes and disease states.[1]