The STK4 gene contains 11 exons. The sizes of the exons 1-11 are 68, 81, 129, 115, 165, 168, 138, 129, 192, 154, and 585 bps. Exon 1 contains the 5 untranslated region and the translation initation ATG, and a few additional codons. Exon 11 contains the stop codon and the 3 untranslated region. Other features of the STK4 gene, such as promoters or enhancer elements, have not been described.

A 7 kb transcript is detected in many tissues with highest steady state levels in the thymus amd bone marrow. The predominant human STK4 mRNA encodes an open reading frame of 1883 bases, resulting in a predicted proteins of 487 amino acids.

STK4 is a member of the GC kinase group of the STE20 family of serine/threonine protein kinases. STK4 homodimerizes through a C-terminal motif, and removal of the C terminus results in marked activation of the kinase. STK4 is cleaved by caspases during apotosis, releasing an active 34 kD kinase fragment. STK4 associates with the WW-domain protein Salvadore, which may link STK4 to the LATS tumor suppressor pathway.

Widely expressed in both embryonic and adult tissues.

Nucleus and cytoplasm. In the nucleus, STK4 phosphorylates Histone 2B at Ser 14, a modification associated with chromosome condensation in apoptotic cells.

STK4 plays a role in promoting apotosis, in particular, in chromosome condensation during programmed cell death. STK4 is cleaved by caspase 3 during apoptosis, releasing the highly active N-terminal kinase domain. This active protein promotes apoptosis by activating JNK and also by further caspase activation. STK4, and/or the highly related protein , may act as tumor suppressors, acting downstream of Raf.

STK3 (a.k.a. MST2, KRS1).