Preferential Resistance of Phosphodiester Bonds between Deoxycytidine and 5′-Adjacent Bases toChlamydomonasNuclease C

摘要

ChlamydomonasCa2+-dependent nuclease (nuclease C) has been shown to be polymorphic (Ogawa and Kuroiwa 1985a). Aged preparations of crude extract obtained in the absence of protease inhibitor contained little nuclease C12. Instead, most of the activities appeared in association with smaller molecules similar in size to nuclease C3 and C4 that are members of nuclease C isozymes, suggesting that the polymorphism may be caused by the action of an endogenous protease.Both the original form and the active fragments showed base-specific endo-exonucleolytic activity, and liberated an extremely low level of 3′-dCMP as compared with the other three 3′-dNMPs. We compared the extent of hydrolysis of phosphodiester bonds between two bases of all possible combinations. The result showed preferential resistance of phosphodiester bonds between dC and 5′-adjacent bases to nuclease C. This explains the paucity of 3′-dCMP in the digests of DNA. The base-specific action of nuclease C12 was preserved during the modification by endogenous p