Participation of pre-existing ribosomes in the induced synthesis of β-galactosidase

Abstract

1. The synthesis of ribosomes by a uracil-less mutant of Escherichia coli which was induced to synthesize β-galactosidase (β-d-galactoside galactohydrolase, EC 3.2.1.23) has been investigated during carbon-source and uracil starvation. 2. The study depends upon the separation of 15N-containing ribosomes from 14N-containing ribosomes in a CsCl-density gradient, and upon the separation of ribosomes from messenger RNA in a sucrose-density gradient. 3. It has been found that, under such starvation conditions, there is no synthesis of new ribosomes while the synthesis of messenger RNA continues. 4. It is therefore concluded that pre-existing ribosomes can make a new species of bacterial protein.