Identification and characterization of human PKNOX2, a novel homeobox-containing gene

The three-amino-acid loop extension (TALE) homeodomain proteins are highly conserved transcription regulators. Since cooperative function among member s of this growing family is critical for regulating transcription, we have tried to explore novel members to understand their regulatory mechanisms in cellular proliferation and differentiation. Here we report identification of PKNOX2, a novel TALE homeodomain protein that shows distinct homology wi th PKNOX1, a stable partner of PBX proteins. PKNOX2 is composed of 460 amin o acids and contains HR1, HR2, and homeodomain, which are highly similar to PKNOX1, suggesting that PKNOX2 may also interact with PBX proteins as well as the same DNA sequence as PKNOX1. Genomic organization of PKNOX2 also sh owed high similarity to PKNOX1, though PKNOX2 lies on a different chromosom al region, 11q24. Unlike PKNOX1, which was broadly expressed in many tissue s, PKNOX2 showed a more restricted pattern of mRNA expression. Nuclear loca lization of PKNOX2 was confirmed by transfection of epitope-tagged cDNA. Ta ken together, these data indicate that PKNOX2 is a novel PKNOX-related prot ein and may interact with PBX proteins and play a tissue-specific regulatio n of transcription. (C) 2001 Academic Press.