1. A native DNA fraction was isolated from the young vegetative mycelium of Streptomyces griseus strain No. 52-1 and was compared with a similar fraction of Escherichia coli B. The endogenous RNA polymerase activities of these DNA fractions were examined. 2. Determining the base composition of the 14C labelled RNA synthesized in vitro, it was found that the conversion of 14C UTP into CMP residue of RNA is negligible in the DNA fraction of S. griseus, while it is significant in the DNA fraction of E. coli. By the proof of density gradient centrifugation, the RNA synthesized in vitro was mainly of messenger size in both species. 3. Template activity of the native DNA fractions was investigated in the presence of isolated E. coli RNA polymerase. When measuring the endogenous RNA polymerase and template activities of the DNA complexes at lower and higher ionic strength it was established that DNA complexes of E. coli under both ionic conditions behaved essentially as free DNA strands did, while endogenous and exogenous RNA polymerase activities in DNA complexes of S. griseus are inhibited in medium of lower ionic strength. Our results indicate the presence of some additional compound in the S. griseus aggregate which is absent in E. coli. This compound could function at lower ionic strength while it would be inactivated at higher ionic strength.
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