Importance of membranes in protein biosynthesis

Sucrose-dependent spectinomycin-resistant mutants of Escherichia coli

Spectinomycin-resistant (Spcr) mutants of Escherichia coli were isolated from nutrient agar plates containing 20% sucrose and 100 mug of spectinomycin per ml. About one-third of the Spcr mutants thus obtained were sucrose dependent (Sucd) and were classified into two types: I, those unable to grow on sucrose-free medium in the presence of spectinomycin; and II, those unable to grow on sucrose-free medium irrespective of the presence of spectinomycin. Most of these mutants were hypersensitive to antibiotics, dyes, and detergents and were abnormal in cell morphology, suggesting changes in cell envelopes. Reversion experiments indicated that the sucrose-dependent spectinomycin resistance and hypersensitivity to various chemicals were not independently induced properties. The Sucd-Spcr mutations of type I mutants were transducible by phage P1 and were mapped at the strA-aroE region.

Localization of polyribosomes containing alkaline phosphatase nascent polypeptides on membranes of Escherichia coli

A procedure has been developed for extracting membranes from bacterial cells under conditions that keep a large fraction of bacterial polyribosomes intact. Freeze-thawing spheroplasts in the presence of deoxyribonuclease, followed by differential centrifugation, permits a separation of free and membrane-associated polyribosomes. The latter fraction contains as much as 40% of cell ribosomal ribonucleic acid (RNA) and 55% of cell messenger RNA (mRNA). Nascent polypeptides were divided almost equally between the two fractions, but 70 to 80% of alkaline phosphatase nascent chains, detected both chemically and immunologically, were derived from polyribosomes associated with the bacterial membrane. Analysis of the fractions for mRNA specific for the lac and trp operons by RNA-deoxyribonucleic acid hydridization showed somewhat larger amounts on membrane than on free polyribosomes, but enrichment for nascent alkaline phosphatase (a secreted protein) on membranes was consistently greater, suggesting that polyribosomes making secreted proteins are more tightly bound to membranes. Electron micrographs of the membrane preparations show relatively intact membranes with clusters of polyribosomes on their inner surfaces.

Effect of potassium ions on the attachment of polyribosomes to the membranes in lysates of exponential-phase cells of Bacillus amyloliquefaciens

1. The distribution of ribosomal components between the soluble and membrane fractions of a preparation of exponential-phase cells of Bacillus amyloliquefaciens lysed with lysozyme in 0.05m-tris buffer, pH7.6, containing 0.01m-Mg(2+), was strongly influenced by the addition of K(+) to the buffer, in the range 0-0.1m. 2. In the absence of K(+), 37% of the ribosomal material was bound to the membrane and was not removed by repeated washing with the lysing buffer. The amount of bound material was progressively decreased on increasing the K(+) concentration to 0.1m, when only 5% of ribosomal components remained attached to the membrane. 3. About 87% of the material that remained bound to the washed membranes prepared in the absence of added K(+) was removed on suspension of the membranes in a buffer containing 0.1m-potassium chloride. 4. In the absence of K(+), washed membranes, containing no detectable ribosomal material, were able to re-attach no more than half as much material as was found associated with membranes in the same buffer immediately after lysis. 5. There was no evidence of binding of specific components to the membrane. 6. In the presence of 0.05m-tris buffer, pH7.6, maximum incorporation of amino acids into protein by B. amyloliquefaciens polyribosomes is effected in the presence of 0.01m-Mg(2+) and 0.07-0.1m-K(+), under which conditions less than 10% of the ribosomal material of a cell lysate would be membrane-bound.

Membranes in polyribosome formation by rabbit reticulocytes

When rabbit reticulocytes are incubated with n-butanol, an agent disruptive to the structure and function of cellular membranes, there is a rapid disaggregation of the polyribosomes. Reaggregation is promoted when the n-butanol is diluted below a critical concentration or when the cells are washed free of the alcohol and the incubation is continued. Neither disaggregation nor regeneration will occur in the absence of protein synthesis. These observations suggest that integrity of the reticulocyte membrane is necessary for the attachment of ribosomes to messenger RNA and for the formation of polyribosomes.

Amino acid accumulation and incorporation in rat intestine in vitro

1. Rings of rat jejunum incubated in vitro accumulate a mixture of amino acids at a rate of about 3 mumoles/cm. hr. The rate of incorporation of the accumulated amino acid into the tissue protein corresponds to a rate of synthesis of 50% of the protein of the whole wall in five days.2. Replacement of the Na(+) in the NaCl of the incubation medium by choline or by Li(+) did not prevent amino acid accumulation by the tissue. However, replacement of the Na(+) by K(+) prevented the accumulation.3. The accumulation of amino acids by rat jejunum in vitro proceeded at normal rates not only in the presence in the incubation medium of oxygen tensions below 10 Torr but also in the presence of 2,4-dinitrophenol. Reasons are given for supposing that the findings are compatible with the view that the energy upon which depend the processes of amino acid accumulation by the tissue could be derived from the movement of ions across cellular boundaries.4. The amino acid incorporation into the tissue proteins was reduced to one tenth of the control rate in the presence of 2,4-dinitrophenol or by hypoxia so that the processes of incorporation depend upon energy derived from oxidative metabolism. In the presence of oligomycin the tissue respiration was depressed but the amino acid incorporation into the tissue protein was not inhibited. The view that the amino acid incorporation may be able to function with energy intermediates other than ATP is discussed.