In Drosophila, the patterns of homeotic gene transcription that specify body segment identity are maintained by the polycomb group of repressors and the trithorax group (trxG) of activators. On , Srinivasan and colleagues report that the trxG protein Kismet maintains homeotic gene transcription by facilitating an early step in transcriptional elongation by RNA polymerase II (Pol II). kismet, which is needed for segmentation and for body segment specification, encodes the isoforms KIS-L and KIS-S. The researchers show that KIS-L associates with virtually all sites of transcriptionally active chromatin on salivary gland polytene chromosomes taken from Drosophila larvae. This distribution pattern largely overlaps with that of Pol II. Furthermore, the levels of elongating Pol II and of several elongation factors are reduced on polytene chromosomes from kis mutant larvae. The researchers conclude that KIS-L, unexpectedly given its specialised roles in development, plays a global role in transcription by Pol II.
