Promoter Region of the Transcriptional Unit for Human α1‐Chimaerin, a Neuron‐Specific GTPase‐Activating Protein for p21rac

Abstract

α1‐chimaerin is a neuron‐specific GTPase‐activating protein for p21rac, a protein involved in morphological events. The mRNA is highly expressed in certain brain regions. It is also detected in cultured neuronal, but not in non‐neuronal cells. As a first step towards understanding the mechanisms underlying this regulation, genomic clones containing the 5′‐flanking region of the human α1‐chimaerin transcriptional unit were isolated and characterised. A cluster of multiple transcription start sites of α1‐chimaerin mRNAs was detected by primer‐extension and S1‐mapping analyses. The cluster was mapped to nucleotides −464 to −434 (relative to nucleotide A in the initiation codon) in genomic DNA. The 5′‐proximal region contained no TATA box, initiator motif and Sp1‐binding site. A 210‐bp fragment with approximately 110 bp 5′‐flanking sequence could function as a minimal promoter upon analysis using hybrid chloramphenicol acetyltransferase reporter constructs and transient transfection. Internal deletion and point‐mutation experiments revealed that a GGCCAATC sequence located at nucleotides –519 to –512 was essential for α1‐chimaerin promoter activity. Mobility‐shift assay showed the specific binding of nuclear factor(s) to this region, which was competed by the oligonucleotides corresponding to wild‐type but niot mutant forms. The data also suggest the existence of possible novel CCAAT‐binding factor(s) interacting with the α1‐chimaerin CCAAT box binding site. A cell‐type‐preferred suppressor located in the 5′‐distal region was found which may play a role in controlling neuron‐specific expression of α1‐chimaerin mRNA. These findings of a specific promoter for α1‐chimaerin transcription will facilitate further studies on its neuronal‐specific expression and function. Copyright © 1995, Wiley Blackwell. All rights reserved