molecular cloning and characterization of alpha1soluble guanylyl cyclase gene promoter in rat pituitary cells soluble guanylyl cyclase is a cytosolic enzyme which catalyzes conversion of gtp to the second messenger cyclic gmp the transcriptional regulation at the promoter levels of four soluble guanylyl cyclase subunits termed alpha1 alpha2 beta1 and beta2 is largely unknown in this study we identified the transcription start site of alpha1soluble guanylyl cyclase gene in rat pituitary cells and cloned the 35 kb 5promoter sequence analysis of this tataless promoter revealed the presence of several putativebinding sites for transcriptional factors including ccaat site at 41 to 32 and sp1 site at 34 to 24 transfection of pituitary cells with constructs of variable lengths confirmed the relevance of different promoter regions in the control of transcriptional activity among them the 49 to 156 region was critical for basal transcriptional activity electrophoretic mobility shift assay using nuclear proteins extracted from normal and immortalized pituitary cells indicated that the ccaatsp1 site within the 49 to 156 region was able to specifically interact with ccaatbinding factor and sp1 these two sites were partly overlapped and both of them conferred stimulatory effects the in vivo recruitment of ccaatbinding factor and sp1 was confirmed by chromatin immunoprecipitation these results indicate that the composite ccaatsp1 ciselement contributes to the expression of alpha1sgc subunit in resting pituitary cells