GATA3 is a major regulator of luminal breast cancer, but its DNA-binding behaviour across the diverse GATA motif landscape, and how that binding translates into regulatory signalling, was not well characterised. I evaluated and benchmarked ChIP-seq tools for alignment, peak detection, and de novo motif analysis, built ATAC-seq and RNA-seq pipelines for differential chromatin-accessibility and expression analysis, and integrated the signals to characterise the regulatory landscape.