FC0009
Octamer binding factor 1 (Oct-1)  -  Ig-κ promoter

Biological function
Transcription factor, which binds an octamer motif (5’-ATTTGCAT-3’) and activates the promoters of the genes for some small nuclear RNAs (snRNA) and of genes such as those for histone H2B and immunoglobulins.

Domain organization/sequence features
POU domain transcription factors have two DNA- binding subdomains, connected by a linker, which is 23 residues in case of Oct-1. The optimal binding site of POU domains differs between the family members, suggesting a contribution of the linker to specificity.

Structural evidence
The linker is invisible in the crystal structure of the complex.

Biochemical evidence
Varying the linker length and composition shows that the minimal linker length is 10-14 amino acids and a conserved Glu also affects binding.

Mechanism category
tethering

Isoforms, context-dependence
POU subdomains are expressed in different cell types. Linker flexibility affects specific activation of target genes. The coding sequence for the two subdomains, POUs and POUhd, are separated by an intron in the genome. This could be a potential determinant of linker length if differential splicing of the intron occurs. The Oct-1 linker intron is out-of-frame with the coding sequence thus only alternative splicing of this intron could generate a different functional protein.

Significance
The length and composition of the fuzzy linker determines transcriptional activity of Oct-1 via transient, specific interactions.