Jung M, Dritschilo A, Mark G, Kasid U
Department of Radiation Medicine, Lombardi Cancer Center, Georgetown University, Washington, D.C. 20007.
Biochem Biophys Res Commun. 1993 Jan 29;190(2):462-9. doi: 10.1006/bbrc.1993.1070.
Oncogenic activation of the human c-raf-1 protein (Raf-1) occurs by truncation of its aminoterminus (regulatory domain) and retention of the carboxyterminus (kinase domain). To gain insight into the structure of human raf-1 genomic DNA corresponding to the regulatory domain of Raf-1, we analyzed the nucleotide sequences of introns 4, 8, and 9. Very high frequencies of the direct and indirect repeats, and A/T nucleotides were observed within introns 4, 8, and 9; and the DNA sequences, 5'-TTAGTCA-3' and 5'-TGATTCA-3', like the DNA recognition site of transcription factor AP-1, were identified within intron 4 of raf-1 in human normal and tumor DNAs. In addition, several transcriptional elements (CAAT box, TATA sequences, eukaryotic transcription initiation sites, and cellular transcriptional elements) were found within introns 4, 8, and 9 of human raf-1. These data suggest: 1) the high frequency of intron-specific repeats is a possible recombinational mechanism for derivation of truncated oncogenic forms of Raf-1; and 2) the multiple transcriptional elements within introns 4, 8, and 9 may have important implications in the regulation of raf-1 transcription and, therefore, its role in cell growth and proliferation.
人类c-raf-1蛋白（Raf-1）的致癌激活是通过其氨基末端（调节结构域）的截短和羧基末端（激酶结构域）的保留而发生的。为了深入了解与Raf-1调节结构域相对应的人类raf-1基因组DNA的结构，我们分析了内含子4、8和9的核苷酸序列。在内含子4、8和9中观察到直接和间接重复序列以及A/T核苷酸的频率非常高；并且在人类正常和肿瘤DNA的raf-1内含子4中鉴定出了DNA序列5'-TTAGTCA-3'和5'-TGATTCA-3'，类似于转录因子AP-1的DNA识别位点。此外，在人类raf-1的内含子4、8和9中发现了几个转录元件（CAAT盒、TATA序列、真核转录起始位点和细胞转录元件）。这些数据表明：1）内含子特异性重复序列的高频率是Raf-1截短致癌形式衍生的一种可能的重组机制；2）内含子4、8和9中的多个转录元件可能对raf-1转录的调节具有重要意义，因此对其在细胞生长和增殖中的作用也具有重要意义。
