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It is well know that protein synthesis stopped either by chloromycetin or by starvation of an essential amino acid for a RC relstrain, ribosomal RNA synthesis continues, but products do not appear in 50 S and 30 ribosomes. It has also been shown that 5 S RNA synthesis is altered by the addition of chloromycetin but in an unknown manner. In this paper we report that: (a) during amino-acid starvation of a starvation of RCrel strain of Escherichia coli, 5 S RNA is transcribed as 5 S relax RNA located outside the ribosomes, in the supernatant fraction; (b) this 5 S RNA which is slightly longer than the normal product is convertible into a true 5 S RNA when protein synthesis is restored after blockage of RNA synthesis by actinomycin ;(c) part of the 23 S RNA from a 25 S particle appears after resumption of protein synthesis in a 40 S parcel which contains normal 5S RNA; (d) a pool of 5 S precursor RNA exists outside the 50 S ribosome. This 5 S precursor RNA is isolated; (e) this precursor which is isolated from the 105000xg supernatant fraction after pulse labeling, migrates on gel electrophoresis between 5 S relax RNA and true 5 S RNA. [ABSTRACT FROM AUTHOR]

Phosphatidylserine synthetase occurs in a soluble and a ribosome-bound form in Escherichia coli. The soluble enzyme of E. coli B was partially purified by DEAE-Sephadex chromatography. The ribosomal enzyme was obtained by differential centrifugation. Two types of the enzyme had the same Km (150 μ M) for L-serine. The soluble enzyme was required for the biosynthesis of phosphatidylethanolamine from phosphatidic acid via (CDP-diglyceride in the membrane. The ribosomal enzyme was less effective to the phosphatidylethanolamine formation than the soluble enzyme. By the sucrose-density-gradient centrifugation method the soluble enzyme was proved to be loosely associated with the membrane. [ABSTRACT FROM AUTHOR]