Momota R, Sugimoto M, Oohashi T, Kigasawa K, Yoshioka H, Ninomiya Y
Department of Molecular Biology and Biochemistry, Okayama University Medical School, Japan.
FEBS Lett. 1998 Mar 6;424(1-2):11-6. doi: 10.1016/s0014-5793(98)00128-8.
We first isolated and characterized genomic DNA fragments that cover the 5' flanking sequences of COL4A3 and COL4A4 encoding the human basement membrane alpha3(IV) and alpha4(IV) collagen chains, respectively. Nucleotide sequence analysis indicated that the two genes are arranged head-to-head. To determine transcription start site for COL4A4 gene, we performed RACE and RNase protection assays, indicating that there are two alternative transcripts presumably derived from two different promoters. Interestingly, one transcription start site (from exon 1') of COL4A4 is only 5 bp away from the reported transcription start site of COL4A3, whereas the other transcript (from exon 1) starts 373 nucleotides downstream from the first one, generating the two kinds of transcripts that differ in the 5' UTR regions. Expression of these two transcripts appears tissue-specific; exon 1 transcript was expressed predominantly in epithelial cells, while exon 1' transcript showed rather ubiquitous and low expression. The nucleotide sequence of the promoter region is composed of dense CpG dinucleotides, GC boxes, CTC boxes and a CCAAT box but no TATA box. These results provide information to delineate the promoter activity for the tissue-specific expression of the six type IV collagen genes and basement membrane assembly in different tissues and organs.
我们首先分离并鉴定了基因组DNA片段，这些片段分别覆盖了编码人基底膜α3(IV)和α4(IV)胶原链的COL4A3和COL4A4的5'侧翼序列。核苷酸序列分析表明这两个基因是头对头排列的。为了确定COL4A4基因的转录起始位点，我们进行了RACE和RNase保护分析，结果表明可能存在两种源自不同启动子的可变转录本。有趣的是，COL4A4的一个转录起始位点（来自外显子1'）距离COL4A3报道的转录起始位点仅5个碱基对，而另一个转录本（来自外显子1）则从第一个转录本下游373个核苷酸处开始，产生了在5'非翻译区不同的两种转录本。这两种转录本的表达呈现出组织特异性；外显子1转录本主要在上皮细胞中表达，而外显子1'转录本的表达则较为普遍但水平较低。启动子区域的核苷酸序列由密集的CpG二核苷酸、GC盒、CTC盒和一个CCAAT盒组成，但没有TATA盒。这些结果为阐明六种IV型胶原基因的组织特异性表达的启动子活性以及不同组织和器官中的基底膜组装提供了信息。
