FIG 5.

C. heterostrophus secretes DNases, and secretion is induced by plant tissue. WT, nuc1 mutant, nuc2 mutant, and nuc1 nuc2 double-mutant filtrates degrade intact λ DNA in the presence of plant material. The nuc1 single mutant and nuc1 nuc2 double mutant degrade lambda DNA less well than the WT or the nuc2 single mutant. This indicates that DNase(s) are secreted by the fungus, that the nuc1 mutant secretes a DNase that is important in DNA degradation, and that secretion is induced by host material. Left, size markers in kilobases. +, addition of corn leaf (CL) fragments, lambda DNA, or purified RQ1 RNase-free DNase. Culture filtrates examined were from WT strain C4, nuc1 mutant strains 144206-3-1 and 8-1, nuc2 mutant strains 149183-2-1 and 3-1, and nuc1 nuc2 double-mutant strains 144206/149183-4-1 and 8-1. The negative-control reaction with λ DNA did not degrade the DNA, while the positive-control reaction with λ DNA plus DNase did. Also note that λ DNA was not degraded by the CL material.