Kurt Köhler

Release of repetitive transient potentials and opening of potassium channels by barium in Eremosphaera viridis

A concentration‐dependent effect of Ba2+ on voltage‐independent opening of K+ channels in Eremosphaera was examined. Low concentrations of external Ba2+ (10−2mM) cause the release of repetitive transient potentials. Higher concentrations of Ba2+, however, inhibit these Ba2+‐induced repetitive and also light‐off triggered transient potentials. Experiments with different Ca2+ concentrations in the medium and the treatment with La3+ suggest the interaction of Ba2+ with Ca2+ channels and the participation of internal Ca2+ in the activation of K+ channels.

76-kDa poly(A)—protein is involved in the formation of 48 S initiation complexes

In erythropoietic mouse cells induced by Friend leukemia virus, ≈50% of non‐polyribosomal globin mRNA is found in 48 S initiation complexes ready to be translated. EDTA releases 15 S globin mRNPs, homologous to polyribosomal globin mRNPs. The 76‐kDa poly(A)—protein is one of its main protein components. The other 50% of non‐polyribosomal message can be separated as 20 S ‘free’ mRNPs. Its protein composition is different, especially the 76‐kDa protein is lacking. The role of this protein is discussed.

Evidence for a highly nuclease resistant RNA fragment in prosomes.

Prosomes, small cytoplasmic particles of mouse erythroblasts were found to contain low molecular weight RNA molecules in the range of 80 nucleotides. Nuclease digestion of prosomes suggests that prosomal proteins cover and protect almost the whole length of their RNA(s). Our results demonstrate clearly that RNA is an intrinsic component of prosomes.

Interaction of cytoplasmic messenger-RNA with proteins: their possible function in the regulation of translation

In the present report we summarize recent results concerning our studies on messenger ribonucleoprotein particles and RNA-binding proteins from the cytoplasm of mouse erythroblasts and mouse Krebs II ascites cells.

Selection of prosomes and prosomal RNA by immobilized viral RNAs

Viral messengers were used to select and purify prosomes and prosomal RNA from subribosomal fractions of HeLa cells and mouse erythroblasts. Adenovirus mRNA immobilized on oligo(dT)‐cellulose and tobacco mosaic virus RNA (TMV) sedimenting in sucrose gradients associated strongly with prosomes at high salt conditions forming intermolecular RNA‐RNA hybrids between prosomal RNA and viral RNA. Hybrid selection of small cytoplasmic RNAs with immobilized TMV‐RNA revealed a RNA species migrating at the same position as prosomal RNA. The possible existence of a box‐like sequence involved in hybridization will be discussed.

Prosomes are Involved in the Repression of Viral mRNA

Abstract Prosomes are small cytoplasmic RNP complexes. We present evidence that their RNA is a potential and selective inhibitor of viral mRNA translation while translation of normal cellular mRNA e.g. rabbit globin mRNA or HeLa cell mRNA is not affected.

In vitro reconstitution of messenger ribonucleoprotein particles from globin messenger RNA and cytosol proteins

Deproteinized globin poly(A) + mRNAs reassociate readily in vitro with soluble RNA‐binding proteins of the cytosol; reconstituted messenger ribonucleoprotein complexes are obtained which are very similar to native globin polyribosomal‐mRNP as far as bouyant density in Cs2SO4 and the composition of proteins which can be crosslinked to the mRNA are concerned. Proteins thus identified bind specifically to mRNA and not to ribosomal RNA or any synthetic oligonucleotides, with one exception: a 78‐kDa protein could be cross‐linked to poly(A).

A comparative study by sucrose gradient electrophoresis of messenger ribonucleoprotein complexes.

The recently developed method of sucrose gradient electrophoresis has been used in the investigation of mRNA containing particles prepared in an undenatured state. The particles containing messenger RNA migrate as a homogeneous fraction with a mobility different from that of ribosomal praticles. Informosomes and polysomal mRNPs have about the same mobility. On the contrary artificial complexes, formed by the reaction of cytoplasmic binding factor with RNA, migrate as a heterogeneous fraction. The particles carrying mRNA are drastically and irreversibly affected by a treatment with EDTA. Sodium deoxycholate removes some proteins but seems also to denature them. After treatment by high salt or Sodium deoxycholate the mRNPs migrate as a homogeneous fraction showing that all particles are equally affected.

The Role of Acidic Proteins from Cytoplasmic Fractions of Krebs II Ascites Cells for Efficient Translation

Abstract Acidic proteins with affinity to RNA from cytoplasmic fractions of Krebs II Ascites cells were isolated by means of affinity chromatography on RNA-Sepharose CN-Br-columns. Stepwise elution with 350 mᴍ [K+] and 1000 mᴍ [K+] removed two fractions of proteins both of which are required for the formation of 40S-or 80S-initiation complexes and for efficient translation.

An improved method of sucrose gradient electrophoresis for the study and the separation of ribosomal particles

Abstract The separation of ribosomal particles of differing biological properties can be achieved by electrophoresis on a sucrose gradient column.