*2.2.2 Helix-turn-helix (HTH) proteins*

The ETS, FOX, IRF, HOX, HSF, POU, and PAX proteins belong to the HTH protein group. The HTH domains are present in NANOG, OCT1, PDN, and FLI1 [10]. ETS family proteins [11–13], which bind to GGAA (TTCC)-core motifs, contain ETS domain [14]. They regulate oncogenesis, development, differentiation, and apoptosis. The homeodomain (HD) is classified into 16 major subclasses, including ANTP, HNF, POU, PRD, SIX/SO, and ZF [15]. The HD proteins, including OTFs [16], which consist about 15–30% of TFs in animals, regulate differentiation and development of organisms.
