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Published June 25, 1984 | public
Journal Article

Human dihydrofolate reductase gene organization: Extensive conservation of the G + C-rich 5′ non-coding sequence and strong intron size divergence from homologous mammalian genes

Abstract

The complete human dihydrofolate reductase (DHFR) gene has been cloned from four recombinant lambda libraries constructed with the DNA from a methotrexate-resistant human cell line with amplified DHFR genes. The detailed organization of the gene has been determined by restriction mapping of the cloned fragments and DNA sequencing of all the protein coding regions and adjacent intron segments, and shown to correspond to that of the native human DHFR gene. The gene spans a length of approximately 29 × 103 bases from the ATG initiator codon to the end of the 3′ untranslated region, and contains five introns that interrupt the protein coding sequence. The number and positions of introns are identical to those found in the mouse gene. By contrast, the size of the homologous introns (with the exception of the first one) varies greatly, up to several fold, in the genes from man, mouse and Chinese hamster; the intron sequences also exhibit a great divergence, except in the junction regions. A striking sequence homology, extending over several hundred nucleotides, exists between the human and mouse gene 5′ non-coding regions. These regions are characterized by an unusually high G + C content, 72% and 66% in the human and mouse genes, respectively, which is maintained in the first coding segment and first intron, and is in sharp contrast to the relatively low G + C content (~40%) of the remainder of the gene.

Additional Information

© 1984 Published by Elsevier. Received 12 December 1983, Revised 3 February 1984. These investigations were supported by National Institutes of Health grants (GM11766 and T32 GM07616. We are very grateful to Dr A. Chomyn for carrying out the chromosome preparation and fractionation. B. Maurer for carrying out, some of the genomic blot hybridizations, Dr. F. Almalric (Centre de Recherche de Biochimie et de Génetique Cellulaires du C.N.R.S., Toulouse, France) for help in some of the early mapping studies and valuable discussions, Dr J. Mullins (Department of Microbiology. Harvard University) for providing the phage λJ1, Dr T. O. Baldwin (Texas A & M University, College Station. Texas) for providing the strain TB1, and T. Hunkapiller and Dr L. Hood for help in the computer program analysis of the data and for making the best-fit plotting program available to us prior to publication. The excellent assistance of Ms Doris Finch and Ms Arger Drew is gratefully acknowledged.

Additional details

Created:
August 19, 2023
Modified:
October 20, 2023