An Investigation of RNA Synthesis in Anacystis nidulans During Exponential Growth Using Techniques of RNA-DNA Hybridization

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Abstract
RNA isolated from exponential-phase cultures of A. nidulans was used to titrate denatured DNA over a wide range of RNA:DNA ratios. Of A. nidulans DNA, 0.6% was complementary to purified rRNA and 0.062% was complementary to tRNA. Under the growth conditions employed (35.degree. C; mean generation time 4 h), unstable RNA accounted for 40% of the rapidly labeled RNA fraction but only 2% of the randomly labeled RNA fraction. The half-life of the unstable RNA was estimated to be 3% of the mean generation time. A wide variation in the abundance of unstable RNA species was observed; more than 80% of the labeled RNA in both rapidly and randomly labeled unstable RNA fractions was homologous to only 10% of the DNA that was actively transcribed (i.e., 1% of the total DNA). In turn, the actively transcribed DNA comprised only 10% of the total DNA since virtually all the unstable and readily hybridizable RNA fraction (> 99%) from rapidly and randomly labeled RNA would form stable hybrid with it. This indicated that the remaining fraction of the DNA (90%) was infrequently transcribed.

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