The Xq28 chromosomal band represents a C+G-rich region onto which several genes have been mapped. In most cases, the exact relationship between the mapped genes has not yet been established, and neither the regulatory nor the spacer regions between the various transcription units have been defined. In the region around the L1CAM gene (encoding L1 cell adhesion molecule), the transcription units appear, from preliminary analyses, to be quite compact. By sequencing the region at the 3' end of the recently found host cell factor 1-encoding gene (HCFC1), we report that the renin-binding protein-encoding gene (RBP) major transcription start point lies 2763 bp downstream from the 3' end of HCFC1 and that both are transcribed in the same direction from the telomere to the centromere.