The Octamer-binding proteins (Oct) are a group of highly conserved transcription factors that specifically bind to the octamer motif (ATGCAAAT) and closely related sequences that are found in promoters and enhancers of a wide variety of both ubiquitously expressed and cell type-specific genes. Transcriptional regulation of gene expression is dependent on the interactions of transacting proteins with cis-acting sequence-specific DNA elements located in gene promoter or enhancer regions. The octamer motif, ATTTGCAT, and its closely related sequences are a group of cis-acting transcriptional regulatory elements found in the promoters and enhancers of a wide variety of both ubiquitously expressed and cell type-specific genes.  
To date, eight genes that encode these Oct proteins, Oct1, Oct2, Oct3/4, Oct6, Oct7, Oct8, Oct9, and Oct11, have been cloned and characterized. All Oct proteins, like their POU domain-containing family members, share a highly conserved bipartite DNA binding domain, consisting of an approximately 75 amino acid amino-terminal POUS subdomain and a 60 amino acid carboxy-terminal POUH subdomain. These domains are tethered by a linker of variable length. Oct proteins have been known to function as both positive and negative regulators of gene expression. Genes known to be regulated by Oct include a wide variety of ubiquitously expressed genes and tissue-specific genes. Loss of Oct4 changes the fate of the inner cells of the blastocyst of early mouse embryos; these cells cannot form the inner cell mass (ICM) and differentiate into a trophectoderm lineage. Oct7 is essential for the differentiation of specific neuronal lineages in mouse hypothalamus development. In the promoters of many genes, such as β-casein, MMTV, Ig, and lipoprotein lipase, an octamer-binding site is closely present upstream of the TATA box. 
Evidence suggests that Oct proteins may activate transcription of these genes by directly interacting with TATA-binding protein (TBP).  Oct1 and Oct2 have nearly identical DNA binding specificity, and the Ig promoters are equally responsive to both Oct1 and Oct2. Binding of Oct1 or Oct2 to the Ig promoters recruits the B cell-specific coactivator Bob-1/OCA-B/OBF-1. Elevation of cAMP levels enhances Oct1 phosphorylation and shuttles Oct1 from the nucleus to the cytoplasm. Reduced nuclear Oct1 leads to increased expression of Cdx-2, which, in turn, regulates proglucagon and proinsulin expression. Oct7, 8 and 9 are also called brain factors (Brn): Oct7 (Brn2), Oct8 (Brn1) and Oct9 (Brn4).

References

1.Zhao FQ. Front Biosci (Landmark Ed). 2013;18:1051–1071.