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Proc Natl Acad Sci U S A. 1994 Dec 20;91(26):12423-7.

An isoform of transcription factor CREM expressed during spermatogenesis lacks the phosphorylation domain and represses cAMP-induced transcription.

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  • 1Laboratory of Molecular Endocrinology, Massachusetts General Hospital, Harvard Medical School, Howard Hughes Medical Institute, Boston 02114.


cAMP response element-binding protein (CREB) and modulator protein (CREM) regulate the transcription of cAMP-responsive genes via phosphorylation by cAMP-dependent protein kinase A. Reverse transcription and polymerase chain amplification of RNA from male germ cells identify an alternatively spliced CREM isoform, CREM delta C-G, lacking four exons including those encoding the protein kinase A-regulated phosphorylation domain and the flanking glutamine-rich transcriptional activation domains. CREM delta C-G retains exons that encode the basic-leucine zipper (bZIP) DNA-binding domain, binds to cAMP response elements (CREs), and competitively inhibits binding of CREB and CREM to CREs. Expression of CREM delta C-G inhibits transcription of a CRE-containing chloramphenicol acetyltransferase reporter plasmid induced by endogenous CREB. Antiserum to CREM detects CREM delta C-G in elongated spermatids from rat testis. These observations indicate that CREM delta C-G is a unique form of a competitive negative regulator of CREB-mediated gene transcription expressed in a maturation-dependent manner in haploid germ cells. The developmental specificity of CREM delta C-G suggests that it may play a role in transcriptional regulation during spermatogenesis.

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