. The biological role of ribonucleic acids. RNA; Biosynthesis. MICROSOMES AND RNA PARTICLES 19 and protein synthesis were inhibited while DNA synthesis remained unimpaired. Similar conclusions have been drawn by Spiegelman and his co- workers (1955) from a series of extensive experiments on induced enzyme synthesis. They found that strong interference with DNA synthesis has no striking effect on enzyme formation, whereas a 50 % inhibition of RNA synthesis completely suppresses induced enzyme synthesis. Recent experiments of Chantrenne (1956a, b) confirm in a very convincing way that the synthe
. The biological role of ribonucleic acids. RNA; Biosynthesis. MICROSOMES AND RNA PARTICLES 19 and protein synthesis were inhibited while DNA synthesis remained unimpaired. Similar conclusions have been drawn by Spiegelman and his co- workers (1955) from a series of extensive experiments on induced enzyme synthesis. They found that strong interference with DNA synthesis has no striking effect on enzyme formation, whereas a 50 % inhibition of RNA synthesis completely suppresses induced enzyme synthesis. Recent experiments of Chantrenne (1956a, b) confirm in a very convincing way that the synthesis of a specific enzyme protein is associated with the synthesis of a new, possibly specific RNA. He found that, when non-respiring yeast cells synthesize catalase under the inducing action of oxygen, new RNA molecules are built up. Under Chantrenne's (1956a, b) experimental conditions, adenine is incorporated into RNA of adapting cells at a faster rate than in non-adapted cells; furthermore, this incorporation occurs pref- erentially in one particular cell fraction. The evidence, as it now stands, is thus strongly in favor of idea that, in microorganisms, fresh RNA synthesis occurs wk^^l-^-^'^Z ^ new protein synthesis has been induced. ' ''^ -« .:. 4. THE ROLE OF THE MICROSOMES AND\ RIBONUCLEOPROTEIN PARTICLES IN PROTEIN SY We have already seen that RNA is mainly localized in the and in the cytoplasm. A little more will be said now about cyto- plasmic RNA, while the subject of nuclear RNA will be left for Chapter 3. Thanks to the pioneer work of Claude (1943), it is known that the bulk of cytoplasmic RNA, in a homogenate, is associated with small particles, the microsomes. Electron microscopy has helped considerably in our understanding of the real nature of these micro- somes (see Brachet, 1957, and Haguenau, 1958, for detailed re- views of the question). In short, the microsomes present in a homog- enate are breakdown products of elaborate cytoplasmic structures, known to
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