PARTIAL CLONE OF THE GENE FOR AS PROTEIN OF THE LAMPREY PETROMYZON-MARINUS, A MEMBER OF THE ALBUMIN SUPERGENE FAMILY WHOSE EXPRESSION IS RESTRICTED TO THE LARVAL AND METAMORPHIC PHASES OF THE LIFE-CYCLE

AS was previously found to be a liver-synthesized serum protein that i s found in the larval (ammocoete), metamorphosing, and juvenile indivi duals during the life cycle of Petromyzon marinus but not in the sexua lly mature upstream-migrant individuals (Filosa et al. [1982] Comp. Bi ochem. Physiol., 72B:521-530; [1986] Comp. Biochem. Physiol., 83B:143- 149; Ito et al. [1988] J. Exp. Zool., 245:256-263). In the present wor k, a partial clone for the gene for the AS protein was isolated from a cDNA expression library made from ammocoete liver. Northern blots usi ng this clone showed hybridization with mRNA from the intervals of the life cycle prior to the upstream-migration period but not from the up stream-migration period itself. The cloned DNA was sequenced and the d educed amino acid sequence was found to have 40% identity with an albu min (our SDS-1 protein) from the upstream migrants of P. marinus (Gray and Doolittle, [1992] Protein Sci., 1:289-302), which is homologous t o mammalian serum albumin. Thus the lamprey has two genes, AS and SDS- 1, that code for different but similar albumin-like proteins, which pr edominate at different phases in its life cycle. It is suggested that AS protein, because it is present only at the earlier phases of the li fe cycle and because its gene is transcribed only during this same per iod, may be an early version of the a-fetoprotein (AFP) of mammals tha t is found only in the embryonic, fetal, and neonatal phase of their l ife cycle. (C) 1998 Wiley-Liss, Inc.