Conservation of the tandem arrangement of alpha 1-microglobulin/bikunin mRNA: cloning of a cDNA from plaice (Pleuronectes platessa).

alpha 1-Microglobulin and bikunin are both plasma proteins which are synthesized in mammalian liver from a common mRNA with tandemly arranged coding sequences. Here, we report a piscine homologue of mammalian alpha 1-microglobulin/bikunin mRNA which was serendipitously isolated from a plaice (Pleuronectes platessa) liver cDNA library. The piscine cDNA recognized an approximately 1300 nucleotide mRNA on Northern blots of plaice liver RNA and, to a lesser extent, on blots of kidney and whole blood RNA. The deduced amino acid sequence displayed very similar tandemly arranged and homologous sequences for alpha 1-microglobulin and bikunin to those found in the corresponding mammalian cDNAs (35-38% amino acid identity for alpha 1-microglobulin and 45-50% for bikunin). Southern blots of plaice genomic DNA demonstrate that there are probably no closely related genes in addition to the gene for this cDNA. Taken together, these results suggest that the structure of the alpha 1-microglobulin/bikunin mRNA and gene is conserved in fish and mammals, implying an important common function for the tandem expression of these proteins.