INTERRELATIONSHIP BETWEEN 2 FORMS OF DNA-POLYMERASE-ALPHA FROM EGGS OF THE TELEOST FISH MISGURNUS-FOSSILIS L (LOACH)

Two forms of DNA polymerase a, namely, alpha(1) and alpha(2), have bee n isolated from eggs of the teleost fish Misgurnus fossilis (leach). T hese enzyme forms have nearly the same molecular weight (similar to 17 0 kD) but differ in their affinity for DEAE-Toyopearl ion-exchange res in. Both farms were free from primase and 3'-->5'-exonuclease activiti es. The form alpha(2) which was predominant in the eggs and early embr yos, was purified to a nearly homogeneous state. It consisted of a pol ypeptide of molecular weight 168 kD which is presumed to be the cataly tically active subunit of DNA polymerase alpha. On the basis of the ch anges in the activities of the two forms of DNA polymerase a during em bryogenesis, it is suggested that form alpha(1) is a product of posttr anslational modification of the original form alpha(2) The form alpha( 2) was treated with different enzymes, including protein kinase C, alk aline phosphatase, and some proteases (trypsin, aminopeptidase, and ca rboxypeptidases A and B) to test this hypothesis. The experiments show ed that an enzyme form with the properties typical of form alpha(1) co uld be obtained from the original form alpha(2) upon limited proteolys is by carboxypeptidases A and B. Thus, a structural rearrangement of D NA polymerase alpha in leach eggs and embryos due to limited proteolys is of a catalytic subunit from the carboxyl terminus is a probable mec hanism for posttranslational modification of the enzyme.