Studies of specificity of deoxyribonuclease II from thymus.

The early studies on the specificity of different deoxyribonucleases (DNases) have been reviewed by Schmidt (2). Since that time, digests of deoxyribonucleic acid (DNA) by DNase I and DNase II were compared in respect to the size of fragments (3). More recently, a partially purified DNase from Micrococcus pyogenes (4) has been shown to produce fragments terminated in 3’-phosphate (4, 5). Independently, and almost simultaneously, in Sinsheimer’s laboratory, Koerner (6) concluded that DNase II from spleen also produced fragments terminated in 3’-phosphate. Besides the specificity toward the 5’-bond of the diphosphate linkage, no other specificity requirements were observed for the latter enzyme. A study of a similar DNase II from thymus, presented in this paper, also leads to the conclusion that the reaction products are terminated in 3’phosphate. Furthermore, it will be shown that the sequence’ Pyp-Pup is absent from the products, thus suggesting that this linkage is preferentially attacked by DNase II.