Study of extracellular ribonuclease activity in ustilago hordei

Extracellular ribonuclease activity was detected in culture media of sporidial and mycelial cultures of Ustilago hordei. The RNase activity was maximal at pH 5.0, 6.5 and 8.0. The secretion of the RNase activity was a function of the cell density. Release of pH 4.5 and pH 7.5 activity was coincident. Enrichment of the simple glucose and salts medium delayed the initial secretion of activity. The presence of RNA in the medium did not enhance the amount of activity released. Furthermore, since the presence of RNA in the medium was not required for the release of the RNase activity into the medium, it is suggested the synthesis and secretion is a constitutive function. N-methyl-N'-nitro-N-nitrosoguanidine was used to produce auxotrophic strains. Selection methods for the detection of strains deficient in extracellular RNase activity are discussed.Science, Faculty ofBotany, Department ofGraduat