The L63 gene is necessary for the ecdysone-induced 63E late puff and encodes CDK proteins required for Drosophila development

The pulse of ecdysone that triggers Drosophila metamorphosis activates six early genes in a primary response made visible by polytene chromosome puffs . The secondary response is detected by the induction of over 100 late puff s, only a few of which have been subject to molecular genetic analysis. We present a molecular and mutational analysis of the L63 gene responsible for the late puff at 63E. This gene contains overlapping L63A, B, and C transc ription units of which the A unit encodes two isoforms and the B unit three . The C unit, which exhibits little activity, encodes one of the B isoforms . Evidence that L63B, but not L63A, transcription is ecdysone responsive de rives from their developmental transcription profiles and from P-element mu tagenesis showing that ecdysone induction of the 63E puff requires sequence s adjacent to the 5' end of L63B but not those adjacent to the 5' end of L6 3A. L63-specific lethal mutations showed that L63 is required not only for metamorphosis, but also maternally and for embryonic and larval development . The L63 proteins contain a common C-terminal 294-aa sequence that is 71% identical to the CDK sequence of the murine PFTAIRE protein. In vivo tests of L63 proteins altered by site-directed mutagenesis showed that they exhib it CDK functions. L63 proteins are widely distributed among late larval and prepupal tissues and are unlikely to be involved in cell cycle functions. (C) 2000 Academic Press.