Heterochromatin-mediated gene silencing is not affected by Drosophila CBP activity

Cyclic AMP Response Element Binding protein (CREB)-binding protein (CBP) is an acetyltransferase important for modifying histones and chromatin-associated proteins and thus affecting transcription and other DNA metabolic processes. We found that the Drosophila CBP (dCBP) is associated with the NAD(+)-dependent deacetylase, SIR2, which was originally identified as a silencing information regulator in yeast that models silenced and repeated sequence chromatin such as centric heterochromatin, telomeres, and the repeated rDNA sequences. As in yeast, Drosophila sir2 (dsir2) affects the formation and/or function of centric heterochromatin. The fact that we found dCBP in immunecomplexes with dSIR2 in vivo and found that dCBP can interact with dSIR2 directly in vitro suggested that dCBP might affect the packaging of silencing heterochromatin as well. A careful study of the dCBP mutations provides evidence that dCBP does not affect the formation and/or function of centric heterochromatin and thus may affect other dSIR2 functions.