Abstract
A nuclease from N. crassa mycelia was found to attack both heat-denatured and native DNA in endonucleolytic manner. The products of exhaustive degradation of heat-denatured DNA were mainly di- to pentanucleotides bearing 5'-phosphoryl groups. 5'-Mononucleotides amounted to 4.4% of the total products and the base distribution was in the following order: dTMP_??_dCMP>dGMP>dAMP. Analysis of the residues at 5'- and 3'-termini of the oligonucleotides showed that thymidine was predominant at both termini, especially at 3'-termini. Also the analysis of terminal residues produced by limited digestion (27% and 55.5% of the substrate were rendered acid soluble, respectively) gave the same results as above. Therefore, it was suggested that N. crassa nuclease has some preference for thymidine residue to hydrolyze the sequence of -T↓pT- or -T↓pX- predominantly. The activity toward synthetic polymers was in the following order; poly d(A-T)_??_poly dA•poly dT>poly d(G-C)>poly dG•poly dC. The correlation between GC-contents and the activity was also investigated.
