[en] The human genes coding for growth hormone (hGH) and placental lactogen (choriosomatomammotropic
hormone [hCS]) are clustered on chromosome 17 in the following order 5' hGH-N hCS-L hCS-A hGH-V
hCS-B 3'. So far, a single placenta-specific enhancer has been identified in the locus, 2 kb downstream from
the hCS-B gene, and shown to comprise one in vitro binding site for a nuclear protein. We here provide
evidence that the hCS-B enhancer is more complex: (i) protection against DNase I digestion in the 3' flanking
region of the hCS-B gene reveals four binding sites (DF-1, DF-2, DF-3, and DF4) for nuclear proteins from
either placental or HeLa cells, and (ii) placenta-specific enhancer activity can be fully exerted in transient
expression experiments by a 126-bp fragment comprising the DF-3 and DF-4 protein-binding sites. By
dissecting this region, we show that enhancer activity is mediated by a synergy between DF-3 and DF-4.
Competitions with various oligonucleotides in footprinting and gel retardation experiments indicate that the
same protein or set of proteins, different in HeLa and placenta cell nuclei, interacts with sites DF-2, DF-3, and
DF-4. We also studied the regions of the hCS-L and hCS-A genes which are highly similar to the hCS-B
enhancer.
