Four splice variants (alpha I-IV) of the stress-activated protein kinase JNK/SAPK alpha-isoform have been identified in the mouse. One of them (alpha I) contains an open reading frame of 1269 bp encoding a potential protein of 423 amino acids, whereas the second variant (alpha II) differs in a region encoding 31 amino acids located in subdomain IX. alpha III lacks this region and also differs in the terminal portion of the 3' untranslated region (3' UTR). A fourth variant (alpha IV) which lacks a region of 41 amino acids located in subdomain IX has also been identified. These splice variants are differentially expressed in mouse tissues: alpha I is the most abundant in brain areas, whereas alpha II is mainly expressed in extracerebral tissues, such as liver; alpha III and alpha IV are present in brain and other tissues although in lower amounts.