is a member of the keratin gene family. The type II hair keratins are clustered in a region of chromosome 12q13 and are grouped into two distinct subfamilies based on structure similarity. The predicted protein has 494 amino acids. The amino acid sequences of HB1, HB3, HB5, and HB6 are extremely conserved in the alpha-helical, N-terminal, and proximal C-terminal domains. HB3 is more closely related to HB1 and HB6 than to HB5. In situ hybridization studies demonstrated that type II keratin genes are sequentially activated in the hair follicle in the following order: HB5--(HB1, HB3)--HB6. Both HB1 and HB3 mRNA syntheses begin 10 to 15 cell layers above the apex of the dermal papilla and end abruptly in the middle of the cortex.