Serine/threonine kinase 11 or LKB1 is a protein kinase which in humans is encoded by the STK11 gene. The STK11/LKB1 gene, which encodes a member of the serine/threonine kinase, regulates cell polarity and functions as a tumour suppressor Smith et al. (1999) found that the mouse Lkb1 gene encodes a protein showing strong sequence similarity to human LKB1. Karuman et al. (2001) demonstrated that LKB1 physically associates with p53 (191170) and regulates specific p53-dependent apoptosis pathways. Jenne et al. (1998) determined that the STK11 gene extends over 23 kb of genomic DNA and is composed of 9 exons, which are transcribed in telomere-to-centromere direction. Smith et al. (1999) found that the mouse Lkb1 gene consists of 10 exons covering approximately 15 kb.