Hayashi K, Makino R, Kawamura H, Arisawa A, Yoneda K
Nucleic Acids Res. 1987 Aug 25;15(16):6419-36. doi: 10.1093/nar/15.16.6419.
Rat genomic regions covering c-myc were cloned from the DNA of both normal liver and two lines of Morris hepatomas, one of which had c-myc amplification. The three restriction maps showed perfect agreement within the overlapping regions. The 7 kb regions, which included the entire normal rat c-myc and the region 2.2 kb upstream, and one from the hepatomas, were sequenced and found to be identical. The coding regions of exons 2 and 3 were highly conserved between rat, mouse and man, but some differences in amino acids were noted. Exon 1 and the non-coding region of exon 3 showed limited homology between the three species. Rat exon 1 contained several nonsense codons in each frame and no ATG codon, indicating there to be no coding capacity in this exon. The 2.2 kb upstream regions and the introns compared showed unusual conservation between the rat and human genes. Some motifs, previously proposed as having a functional role in human c-myc, were also found in equivalent positions of the rat sequence. Nucleas S1 protection mapping revealed the second promoter to be preferentially used in most tissues or in hepatoma cells, and the second poly A addition signal to be the only one functional in all the RNA sources examined.
从正常肝脏以及两株莫里斯肝癌细胞系（其中一株有c-myc扩增）的DNA中克隆出覆盖大鼠c-myc的基因组区域。这三张限制性酶切图谱在重叠区域完全一致。对包含整个正常大鼠c-myc及其上游2.2 kb区域的7 kb片段，以及一个来自肝癌细胞系的相同片段进行测序，发现它们完全相同。外显子2和3的编码区在大鼠、小鼠和人类之间高度保守，但氨基酸存在一些差异。外显子1和外显子3的非编码区在这三个物种之间显示出有限的同源性。大鼠外显子1在每一阅读框中都包含几个无义密码子，且无ATG密码子，表明该外显子无编码能力。比较大鼠和人类基因的2.2 kb上游区域及内含子，发现它们存在异常保守性。一些先前认为在人类c-myc中具有功能作用的基序，在大鼠序列的相应位置也被发现。核酸酶S1保护图谱显示，第二个启动子在大多数组织或肝癌细胞中被优先使用，并且第二个聚腺苷酸添加信号是所有检测的RNA来源中唯一具有功能的信号。
