A cDNA encoding the Drosophila melanogaster p90 ribosomal S6 kinase II (RSK) was isolated from an eye-antennal imaginal disc library and sequenced. The conceptually translated protein is 60-63% identical to vertebrate RSK homologs and contains a perfectly conserved mitogen-activated protein kinase phosphorylation site. The gene was mapped to the base of the X chromosome in division 20 by in situ hybridization to polytene chromosomes.
