Masters J N, Yang J K, Cellini A, Attardi G
J Mol Biol. 1983 Jun 15;167(1):23-36. doi: 10.1016/s0022-2836(83)80032-1.
The presence of dihydrofolate reductase (DHFRase)-specific sequences that, in contrast to the normal DHFRase gene, are not amplified in a methotrexate-resistant cell line, has been detected in the DNA from human sperm and from several human cell lines. DNA fragments containing some of these sequences have been isolated from a cosmid library of human sperm DNA. One of these fragments contains a DHFRase pseudogene (psi HD1) that completely lacks introns, has 92% sequence homology to the corresponding region of normal DHFRase complementary DNA, but exhibits several alterations that make it nonfunctional. The sequence analysis of the inserts of four different plasmids containing the reading frame and varying lengths of the 3' non-coding regions of human DHFRase-specific cDNAs has revealed that the 3' non-coding segments all are colinear in their corresponding portions. Furthermore, the data indicate that the cDNA of one of the plasmids is probably derived from the smallest of the three main human DHFRase messenger RNAs, the 0.8 X 10(3) base (0.8 kb) mRNA, the cDNA of two others, from the 1.0 kb mRNA, and the cDNA of the fourth, from a longer mRNA. These results are consistent with the idea that the multiple forms of DHFRase mRNA in human cells derive from the same gene by different transcription or RNA-processing events. Moreover, the sequence comparison between the psi HD1 and the different DHFRase cDNAs clearly indicates that, if an mRNA intermediate has participated in the formation of this pseudogene, a form of mRNA larger than the 1.0 kb mRNA, probably the 3.8 kb mRNA, must have been involved.
在人类精子和几种人类细胞系的DNA中，已检测到二氢叶酸还原酶（DHFRase）特异性序列的存在。与正常DHFRase基因不同，这些序列在甲氨蝶呤抗性细胞系中未被扩增。含有其中一些序列的DNA片段已从人类精子DNA的黏粒文库中分离出来。其中一个片段包含一个DHFRase假基因（psi HD1），该假基因完全缺乏内含子，与正常DHFRase互补DNA的相应区域具有92%的序列同源性，但表现出几种使其无功能的改变。对包含人类DHFRase特异性cDNA的阅读框和不同长度3'非编码区的四种不同质粒插入片段的序列分析表明，3'非编码区段在其相应部分均为共线性。此外，数据表明，其中一个质粒的cDNA可能来源于人类三种主要DHFRase信使RNA中最小的一种，即0.8×10³碱基（0.8 kb）的mRNA，另外两个质粒的cDNA来源于1.0 kb的mRNA，第四个质粒的cDNA来源于更长的mRNA。这些结果与人类细胞中多种形式的DHFRase mRNA通过不同的转录或RNA加工事件来源于同一基因的观点一致。此外，psi HD1与不同DHFRase cDNA之间的序列比较清楚地表明，如果一种mRNA中间体参与了该假基因的形成，那么一种大于1.0 kb mRNA的mRNA形式，可能是3.8 kb的mRNA，一定参与其中。
