Alkaline deoxyribonucleases released from Neurospora crassa mycelia: two activities not released by mutants with multiple sensitivities to mutagens.

Three major alkaline deoxyribonuclease (DNase) activities have been identified in sorbose-containing liquid culture medium in which wild-type Neurosporacrassa were grown: DNase A, a Ca++dependent endonuclease of molecular weight 65,000 daltons which has no specificity for single- or double-stranded DNA (ss-DNA or ds-DNA) and no activity with RNA; DNase B, a Mg++-dependent single-strand specific exonuclease of molecular weight 78,000 daltons active with both ss-DNA and RNA; DNase C, a divalent metal ion-dependent endo-exonuclease of molecular weight 65,000 having single-strand specific endonuclease activity with ss-DNA and RNA and exonuclease activity with ds-DNA. Three mutants which were shown previously to have wide spectra of sensitivities to mutagens, and which exhibited reduced release of DNase activity on sorbose-containing agar test plates (the Nuh phenotype), were deficient relative to the wild-type in the release of these major alkaline DNases into the liquid culture medium. The uvs-3 mutant released only small amounts of DNase A and DNase C; nuh-4 did not release detectable DNase C and released only a very low level of DNase B; uvs-6 released only a low level of DNase A. A nuh mutant (nuh-3) which is not mutagen sensitive relative to the wild-type released low levels of DNase B. On the other hand, an ultraviolet light-sensitive mutant (nuc-2) which does not have the Nuh phenotype was normal in the release of these DNases.