Kruppel-like factor 18 (KLF18), or Krueppel-like factor 18, is a product of a chromosomal neighbor of the KLF17 gene and is likely a product of its duplication. Phylogenetic analyses revealed that mammalian predicted KLF18 proteins and KLF17 proteins experienced elevated rates of evolution and are grouped with KLF1/KLF2/KLF4 and non-mammalian KLF17. KLF18 has been found in the human testis, though it was previously hypothesized to be a pseudogene in extant placental mammals. Mouse KLF18 expression data indicates that it may function in early embryonic development. It belongs to a family of proteins, called the Specificity Protein (SP)/KLF family, characterized by a C-terminal DNA-binding domain of 81 amino acids consisting of three Kruppel-like C2H2 zinc fingers. These factors bind to a loose consensus motif, namely NNRCRCCYY (where N is any nucleotide; R is A/G, and Y is C/T), such as the recurring motifs in GC and GT boxes (5'-GGGGCGGGG-3' and 5-GGTGTGGGG-3') that are present in promoters and more distal regulatory elements of mammalian genes. Members of the KLF family can act as activators or repressors of transcription depending on cell and promoter context. KLFs regulate various cellular functions, such as proliferation, differentiation, and apoptosis, as well as the development and homeostasis of several types of tissue. In addition to the C-terminal DNA-binding domain, each KLF also has a unique N-terminal activation/repression domain that confers specificity and allows it to bind specifically to a certain partner, leading to distinct activities in vivo. This model represents the N-terminal domain of KLF18. Some KLF18 isoforms have duplicated N-terminal domains.