Figure 7. Autoregulation model.

The earliest roX1 transcripts (red) made at blastoderm originate from an uncharacterized MSL-independent promoter. This RNA may assemble with MSL protein subunits to produce the first functional MSL complexes needed to bind the internal DHS enhancer that drives sustained transcription (blue) from the male-specific promoters. When present, roX2 RNA can also drive roX1 transcription. Components of the replication pre-initiation complex also bind the DHS sequence in male cells (Figure S8A). The msl2 transcripts are made predominantly during replication and new MSL2 protein is needed to assemble and stabilize newly made roX1 RNA.