The MAP kinase‐activated protein kinase 2 contains a proline‐rich SH3‐binding domain

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Abstract
The protein sequence of MAP kinase‐activated protein kinase 2 (MAPKAP kinase 2) deduced from mouse cDNA sequence reveals structural features of the enzyme, which could be of importance for its function: a proline‐rich SH3‐binding domain N‐terminal to the catalytic region, a MAP kinase phosphorylation site and a bipartite nuclear targeting sequence located C‐terminal to the catalytic region. The catalytic domain itself has the strongest homology to calcium/calmodulin‐dependent protein kinase II. Northern blot analysis demonstrates a 3.5 kb MAPKAP kinase 2 transcript which is ubiquitously expressed and, hence, co‐expressed with the mRNA of the recently identified substrate Hsp25 in all tissues analysed. However, the functional consequences of the nuclear targeting sequence present in MAPKAP kinase 2 suggest the existence of further substrates for the enzyme in the nucleus.