The treatment of quiescent cells with growth factors results in the transcriptional activation of the D-type cyclin genes during G1. Expression of the members of this family of cyclins, D1, 2 and 3, is spatially and temporally regulated with respect to growth factor receptor ligation. Transcription of these particular cyclins is proposed to monitor the growth factor signal and the encoded proteins participate in G1 progression. I have been defining the cis-acting elements and trans-acting factors that control transcription of the human cyclin D3 gene in T-cells. Genomic clones for the human cyclin D3 gene, isolated from a human chromosome 6 library, were analysed by restriction endonuclease digestion and a sub-clone extending 1.7kb upstream of exon 1 was sequenced and studied. The human cyclin D3 gene has a TATA-less promoter and a single dominant initiation site. The minimal cyclin D3 promoter sequence was identified as a region 173bp upstream of the transcription initiation site. Transient transfections using CAT (chloramphenicol acetyltransferase) reporter constructs containing sequential deletions of the cyclin D3 promoter defined positively and negatively regulated regions. Transient transfections into Kit225 cells, a human T-cell line whose growth is dependent on interleukin-2 (IL-2), has enabled the definition of sequence conferring responsiveness to IL-2. Preliminary analysis of the proteins binding to these functional regulatory elements has been performed by electrophoretic mobility shift assays (EMSAs). Comparison of these results with those for the cyclin D1 and D2 genes should elucidate how transcription of these genes is co-ordinately regulated by growth factors.