GCN5-independent Rpb4 complexes are highly enriched in decondensed chromosome puffs so may play a role in RNA polymerase II-dependent transcription. Interacts with Pcaf/GCN5 as part of a GCN5-containing ADA (GNAT) multiprotein complex (PubMed:12482983, PubMed:12697829). Component of the Ada2a-containing (ATAC) complex composed of at least Ada2a, Atac1, Hcf, Ada3, Gcn5, Mocs2B, Charac-14, Atac3, Atac2, NC2beta and wds (PubMed:18327268). Expressed both maternally and zygotically throughout development with lowest expression levels in L2 and L3 larvae, and highest expression levels during pupal development (PubMed:12482983, PubMed:12697829). Highly expressed in all developmental stages, though its abundance decreases in L2 larvae then returns to high levels in pupae (PubMed:19921261). Under heat shock conditions, strongly down-regulated in L2 stage larvae with levels remaining low during the L3 and pupal stages. In second instar larvae, down-regulated 1 hr after starvation and then appears to return to normal expression levels 4 hr after nutritional starvation. This protein is produced by a bicistronic gene which also produces the Rpb4 protein by alternative splicing.