A cDNA encoding a protein kinase, which may be involved in the wound signal transduction pathway, was isolated from Nicotiana tabacum. The cDNA, named WAPK, is 1227 bp in length and contains an ORF of 1017 bp. The ORF encodes a polypeptide of 339 amino acids, with a calculated molecular mass of 38234 Da. Analysis of the deduced amino acid sequence shows that the N-terminal region of WAPK contains a catalytic region composed of eleven subdomains which are typically found in Ser/Thr protein kinases. This region shows 78-84% sequence identity with similar regions of abscisic acid (ABA)-induced and external-stimuli-responsive protein kinases. However, the C-terminal region of WAPK shows little homology with similar regions of Ser/Thr protein kinases, except for a 16-amino acid stretch near the end of the catalytic domain. Kinase assays using a WAPK fusion protein expressed in E. coli revealed that WAPK autophosphorylates on serine residue(s). The WAPK gene is predominantly expressed in flowers, moderately in roots, and poorly in leaves. Transcripts were not detected in stems. The WAPK gene was induced by wounding (within 1.5 h), by abscisic acid (within 0.5 h), and by methyl jasmonate (within 2 h). The induction pattern of WAPK mRNA upon wounding was not affected by treatment with diethyldithiocarbamic acid, a reagent which inhibits jasmonic acid biosynthesis. These results suggest that the WAPK gene is regulated by ABA in the wound signal transduction pathway.