The rate of synthesis of ribosomal protein relative to total protein synthesis (αr) was found to vary during the cell cycle of Escherichia coli B/r. It is greater than the average value in newly arisen daughter cells and below average, when cells near division. The increase of αr follows the initiation of chromosome replication and can be understood as a consequence of the duplication of ribosomal protein genes, since many of them are clustered relatively close to the origin of replication. The variations of αr are being compared with the relative rate of fully induced β-galactosidase synthesis (αlac) over the cell cycle, and possible constitutivity of ribosomal protein genes as proposed by Maaløe (1969) is discussed. If the ribosomal efficiency is constant during the cell cycle, the observed variation of αr implies that the increase in total protein deviates from an exponent by 3% over the cell cycle of E. coli B/r growing in glycerol medium.
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