An intron facilitates activation of the calspermin gene by the testis-specific transcription factor CREM tau

Calspermin is a high affinity Ca2+/calmodulin binding protein that is found only in postmeiotic male germ cells. Our previous studies have shown that the calspermin transcript is produced by utilization of a testis-specific promoter located within an intron of the calmodulin kinase IV gene. This promoter contains two cAMP response element-like motifs that bind the testis-specific transcription factor CREM tau. This interaction is required for transcriptional activation. Here we describe a novel regulatory element, the 111-base pair first intron of the calspermin gene, which is also required for enhancement of transcription by CREM tau via the cAMP response element motifs. Deletion or inversion of this intron results in loss of CREM tau-mediated stimulation of transcription. However, CREM tau stimulates calspermin promoter activity when the intron is moved upstream of the promoter but only when inserted in the proper orientation. Footprint, linker scanning, and deletion analyses were used to identify regulatory elements in the intron. We suggest that the intron functions as an orientation-dependent but position-independent regulatory element to activate the calspermin promoter by facilitating the stimulatory effect of CREM tau on transcription.