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The former annotated human pseudogene dihydrofolate reductase-like 1 (DHFRL1) is expressed and functional
Gráinne McEntee, Stefano Minguzzi, Kirsty O'Brien, Nadia Ben Larbi, Christine Loscher, Ciarán Ó'Fágáin and Anne Parle-McDermott
Proceedings of the National Academy of Sciences of the United States of America
Vol. 108, No. 37 (September 13, 2011), pp. 15157-15162
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/41352062
Page Count: 6
You can always find the topics here!Topics: Messenger RNA, Enzymes, Mitochondria, Pseudogenes, Amino acids, Genes, Enzyme activity, Phenotypes, Cell cycle, Gene expression regulation
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Human dihydrofolate reductase (DHFR) was previously thought to be the only enzyme capable of the reduction of dihydrofolate to tetrahydrofolate; an essential reaction necessary to ensure a continuous supply of biologically active folate. DHFR has been studied extensively from a number of perspectives because of its role in health and disease. Although the presence of a number of intronless DHFR pseudogenes has been known since the 1980s, it was assumed that none of these were expressed or functional. We show that humans do have a second dihydrofolate reductase enzyme encoded by the former pseudogene DHFRP4, located on chromosome 3. We demonstrate that the DHFRP4, or dihydrofolate reductase-like 1 (DHFRL1), gene is expressed and shares some commonalities with DHFR. Recombinant DHFRL1 can complement a DHFR-negative phenotype in bacterial and mammalian cells but has a lower specific activity than DHFR. The Km for NADPH is similar for both enzymes but DHFRL1 has a higher Km for dihydrofolate when compared to DHFR. The need for a second reductase with lowered affinity for its substrate may fulfill a specific cellular requirement. The localization of DHFRL1 to the mitochondria, as demonstrated by confocal microscopy, indicates that mitochondrial dihydrofolate reductase activity may be optimal with a lowered affinity for dihydrofolate. We also found that DHFRL1 is capable of the same translational autoregulation as DHFR by binding to its own mRNA; with each enzyme also capable of replacing the other. The identification of DHFRL1 will have implications for previous research involving DHFR.
Proceedings of the National Academy of Sciences of the United States of America © 2011 National Academy of Sciences