THE DROSOPHILA-MELANOGASTER HOMOLOG OF THE MAMMALIAN MAPK-ACTIVATED PROTEIN KINASE-2 (MAPKAPK-2) LACKS A PROLINE-RICH N-TERMINUS

Recently, a mammalian kinase cascade was discovered that is triggered by stress and heat shock, and leads to the stimulation of mitogen-activated protein kinase (MAPK)-activated protein kinase-2 (MAPKAPK-2). Surprisingly, this process turns out to be independent of the classical MAPK. The stress-induced activation of MAPKAPK-2, in turn, results in the phosphorylation of small beat-shock proteins (Hsp), We have isolated a Drosophila melanogaster (Dm) cDNA encoding a polypeptide that has extensive sequence similarity to the mammalian MAPKAPK-2. As in mammalian MAPKAPK-2, the Dm MAPKAPK-2 possesses a MAPK phosphorylation site and a nuclear targeting sequence located C-terminal to the catalytic domain. However, in contrast to its mammalian counterpart, it lacks the Pro-rich N-terminal region proposed to form Src-homology domain 3 (SH3) binding domains. A 2.4-kb MAPKAPK-2 message is expressed throughout development, while two shorter transcripts of 2.3 and 1.8 kb appear to be specifically expressed in the germline, The 1.8-kb transcript results from the usage of an atypical germline-specific polyadenylation signal (AATATA) located early within the 3' untranslated region. Dm MAPKAPK-2 is located at cytological position 5D in the Dm genome.