MOLECULAR-CLONING OF CDNA-ENCODING A BOVINE SELENOPROTEIN P-LIKE PROTEIN CONTAINING 12 SELENOCYSTEINES AND A (HIS-PRO) RICH DOMAIN INSERTION, AND ITS REGIONAL EXPRESSION

When cDNA containing proteins enriched in the bovine cerebellar cortex were cloned, a clone which seemed to encode a selenoprotein P-like pr otein was isolated. The coding nucleotide sequence of its cDNA insert displayed high homology to rat and human selenoprotein P cDNA but cont ained 12 rather than 10 TGAs (12 rather than 10 selenocysteines in ded uced amino acids), a tandem repeat of one CACTCC (His-Ser) and seven C ATCCCs (His-Pro), and a 3' untranslated region approximately 890 bases shorter than that of rat liver selenoprotein P. RT-PCR using a set of primers flanking to the repeat displayed the existense of mRNA withou t the repeat. The tandem repeat and its adjacent region consisted of a similar motif of CAC/TCC/AC/T. Thus, these proteins included a (His-P ro) rich domain with a slightly negative free energy change irrespecti ve of having the tandem repeat or not. Such His-Pro repeats reportedly exist in the segmentation gene paired or homeobox protein Om(1D) of D rosophila. Moreover, both this selenoprotein P-like protein mRNA and s elenoprotein P mRNA were expressed in all the areas of the brain but m ost prominently in the cerebellar cortex, hippocampus, and olfactory b ulb. These findings suggest the possibility that these selenoproteins are major selenium carriers in the brain and play a role in the morpho logical response of nerve or glial cells.