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Xenopus laevis Serum Albumin: Sequence of the Complementary Deoxyribonucleic Acids Encoding the 68- and 74-Kilodalton Peptides and the Regulation of Albumin Gene Expression by Thyroid Hormone during Development^*

Department of Pharmacology, Uniformed Services University of the Health Sciences Bethesda, Maryland 20814-4799
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health Bethesda, Maryland 20892

Address requests for reprints to: Daniel R. Schoenberg, Ph.D., Department of Pharmacology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, Maryland 20814-4799.

Abstract

In adult Xenopus serum, albumin gene expression is regulated by estrogen through the selective destabilization of its mRNA during the vitellogenic response. The present study reports the cDNA sequence of both the 68K and 74K Xenopus albumin mRNAs, their derived amino acid sequence, and the regulation of albumin gene expression during embryogenesis. Albumin mRNA has a 39 nucleotide 5' untranslated region terminating in a consensus translation initiation site. The derived amino acid sequence yields a 24-amino acid hydrophobic leader sequence (terminating in Lys-Arg) that shares significant homology with the leader peptide of rat albumin. Overall there is 37% sequence identity between rat and frog albumin, with exact conservation of all but one Cys residue and the Pro residues responsible for the three domain structure of the mature protein. The 74K albumin (unlike the 68K albumin) is glycosylated; a point mutation converting Lys₂₅₆ to Asn introduces an N-linked glycosylation site that is similar to one found in the sequence of mammalian -fetoproteins. A larval albumin-like protein was not detectable by silver staining in serum of tadpoles before the beginning of metamorphosis at stage 48. Albumin mRNA is absent from early tadpoles (stages 22–47); however, it is rapidly induced at stage 48 as one of the earliest manifestations of metamorphosis. Exposure of embryos to 10^–8 M T₃, which regulates amphibian metamorphosis, resulted in the premature induction of albumin mRNA, such that it is evident by stage 43.

FOOTNOTES

This work was supported by Grants GM-38277 from the NIH and CO7577 from the Uniformed Services University (to D.R.S.). The experiments reported herein were conducted according to the principles set forth in the Guide for the Care and Use of Laboratory Animals, Institute of Animal Resources, National Research Council, DHHS Publication (NIH) 78-23. All recombinant organisms and molecules were handled under conditions of the NIH guidelines for recombinant DNA research. The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or reflecting the views of the Department of Defense or the Uniformed Services University of the Health Sciences.

^* GenBank Accession no.: 68K albumin, M18350; 74K albumin, M21442.

Received for publication November 10, 1988. Revision received December 14, 1988. Accepted for publication December 15, 1988.

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