LIM-kinase 1 and LIM-kinase 2 (LIMK1 and LIMK2) are members of a novel protein kinase subfamily containing LIM motifs at the N-terminus, There are two isoforms of Limk2 transcripts coding proteins with distinct N-terminal structures: LIMK2a, containing two LIM motifs, and LIMK2b, with one and one-half LIM motifs. Here we report the cDNA and genomic structures of mouse LIMK2. The deduced 638-amino-acid sequence of mouse LIMK2a shows 98% identity with that of rat LIMK2a. The mouse Limk2a gene consists of at least 16 exons and spans more than 50 kb. Exon/intron boundaries of the mouse Limk2a gene are exactly conserved with those of the mouse Limk1 gene. An additional exon encoding the Limk2b-specific 5'-terminal sequence was found to be located between exons 2 and 3, suggesting that Limk2a and 2b mRNAs are transcribed from a single Limk2 gene by an alternative usage of exons near the 5' end of the gene. Limk2a and Limk2b transcripts were expressed at different ratios in a variety of mouse tissues. (C) 1997 Academic Press.