期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1982
卷号：79
期号：23
页码：7435-7439
DOI：10.1073/pnas.79.23.7435
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Three groups of recombinant bacteriophage containing coding sequences for dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3 ) were isolated from two human DNA clone libraries. One recombinant (lambda hDHFR-1) contains three exons that encode the COOH-terminal portion of human DHFR. The other two human DHFR genes (hDHFR-psi 1 and hDHRF-psi 2) lack introns. hDHFR-psi 2 contains several in-phase termination codons and is only 93% homologous to the normal human DHFR coding sequences, whereas hDHFR-psi 1 has an open reading frame and is virtually identical to the coding sequence of the normal DHFR gene. The region of DNA sequence homology between each intronless gene and the normal DHFR gene extends 2.9 kilobases beyond the end of the coding sequences. At the 3' end of this homologous sequence, each intronless gene has an A-rich tract. The lack of introns and the presence of the 3' A-rich tract suggest that hDHFR-psi 1 and hDHFR-psi 2 were derived from processed RNA molecules. A short DNA sequence, 60 nucleotides 5' to the ATG start codon in lambda hDHFR-psi 2, is directly repeated immediately after the 3' A-rich tract; such terminal direct repeats also flank integrated proretroviruses and transposable DNA elements and are thought to be the hallmark of inserted DNA sequences.
