An earlier described CK2btes gene of Drosophila melano-gasteris shown to encode amale germline speci®c isoformof regulatory bsubunit of casein kinase 2. Western-analysis using anti-CK2btes Ig revealed CK2btes protein in Drosophila testes extract. Expression of a CK2btes± b-galactosidase fusion protein driven by the CK2btes pro-moter was found in transgenic ¯ies at postmitotic stages of spermatogenesis.