THE SEROTONIN 1A RECEPTOR GENE CONTAINS A TATA-LESS PROMOTER THAT RESPONDS TO MAZ AND SP1

The structure and function of the 5'-flanking region of the mouse and human serotonin la receptor gene have been analyzed by RNA 5' end mapp ing, DNA-protein interaction, and transient expression assays. A large number of mRNA 5' termini, detected by mapping 5' ends from mouse bra in RNA, were found dispersed over a region of about 700 base pairs fla nking the receptor coding sequence. Consistent with the apparently het erogeneous pattern of transcription initiation, the flanking DNA seque nce lacked typical TATA box elements and was rich in guanine and cytos ine. The mouse and human 5'-flanking sequences were 63% homologus and similarly organized. A guanine-cytosine-rich DNA sequence motif relate d to the sequence 5'-GGGG(C/A)GGGG-3' was repeated within the 5'-flank ing region and located at or near several mRNA 5' ends. This DNA seque nce motif bound to proteins in a crude HeLa cell nuclear extract. A cD NA encoding a protein that interacts with this sequence was cloned and found to be the MAZ (Pur-1, Zif87) protein. The interaction between M AZ and the receptor gene 5'-flanking region proximal to the protein co ding sequence was examined by DNase I footprinting, and four sites of MAZ interaction were identified. Three of the four MAZ binding sites a lso were shown to interact with transcription factor Sp1. Overproducti on of MAZ or Sp1 in transient transfection assays increased expression directed by the human 5'-flanking sequence, although MAZ was substant ially more effective. This result suggests that MAZ and Sp1 both parti cipate in regulating expression from the serotonin 1a receptor gene pr omoter, and it raises the possibility that MAZ may act at a variety of promoters through the guanosine-cytosine-rich sequences generally tho ught to serve as binding sites for the Sp1 family of transcription fac tors. Analysis of one of the guanosine-cytosine-rich DNA sequences als o revealed that it can serve as a transcription initiator sequence in vitro. This initiator sequence differs from previously characterized i nitiators and may represent a new class of this transcriptional contro l sequence.