Effect of the presence of a pCpCpCA 3′-terminus in Phe-tRNAPheyeast on the interaction with elongation factors and with the poly U-ribosome system

Ce n’est certes pas un hasard si dans l’ensemble des textes de Tabucchi une forte concentration autour de la figure de Pessoa s’opère dans la période qui précède Sostiene Pereira (1994), texte-pivot dans l’évolution de sa conception de la littérature. Il est vrai que Pessoa n’est jamais absent de l’œuvre de Tabucchi, mais le poète de l’inquiétude métaphysique devient, après Il Filo dell’orizzonte (1986), pour un moment, très présent. Requiem (1991 ; 1992 en traduction italienne) est le point culminant de cette montée pessoienne qui se termine par Gli ultimi tre giorni di Fernando Pessoa (1994). Cette contribution examine quelques aspects de ce sursaut d’attachement et, en premier lieu, se propose d’approfondir le problème des liens entre les visions du monde respectives des deux auteurs

Studies on the initiation of protein synthesis in mouse myeloma tumors

35S- and 3H-labeled short, nascent peptides have been extracted from mouse myeloma ribosomes after incubation of myeloma fragments with [35S]methionine and [3H]amino acids. Edman analysis of these peptides reveals that most of the methionine is present at the N terminus but that other N-terminal amino acids are also present. Light chains synthesized by the RPC-20 tumor fragments were purified from ribosomes, cell sap (released light chain) and the incubation medium (secreted light chain). Ribosome-bound light chains were found to possess some N-terminal methionine whereas released and secreted light chains did not. Since methionine is not the N-terminal amino acid of light (L) chains purified from the urine of tumor-bearing mice, the results indicate that methionine initiates L chain biosynthesis in the myeloma.Total nascent 35S-labeled peptides were extracted from myeloma ribosomes and fractionated on Sephadex G-50. Edman analysis of Chromatographic fractions of varying sizes indicated that the percentage of N-terminal methionine decreased with increasing chain length. This behavior is expected if methionine serves as an initiator amino acid but is removed before completion of the polypeptide chain on the ribosome.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22179/1/0000610.pd

A study of a mutant elongation factor properties of E. coli HAK88 and its mutant elongation factor Tu

The E. coli chromosome contains two genes for elongation factor Tu, tufA (near the fusidic acid resistance marker) and tufB (near the rifampicin resistance marker). It has been discovered that the mutant E. coli K12 strain HAK88 bears a mutation in the tufB gene, which leads to the synthesis of a protein of increased acidity. To determine whether the mutation has altered the protein's function in peptide chain elongation, we have compared the reactivities of normal tufA EF-Tu and mutant tufB EF-Tu (purified together from HAK88) with the components of the AA-tRNA binding cycle. Normal tufA EF-Tu and mutant tufB EF-Tu are indistinguishable in their affinities for GDP, EF-Ts, and phe-tRNA, and differ only slightly in their affinities for ribosomes. Coupled with the results of a separate study showing the similarity of the normal tufA and tufB gene products, these experiments demonstrate that the mutation has not altered the function of tufB EF-Tu in peptide chain elongation. Contrary to the original report (Kuwano et al., 1974; J. Mol. Biol. 86 , 689–698) the HAK88 strains we have examined no longer possess a temperature-sensitive EF-Ts. The growth rates of HAK88 strains resemble the parent HAK8 strain in their lack of tRNA dependence but unlike HAK8 show varying degrees of temperature sensitivity. We conclude that HAK88 contains a physically altered but functionally intact tufB EF-Tu. The mutation in tufB should be valuable for studying in vivo the control of expression of the genes for EF-Tu.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47543/1/438_2004_Article_BF00401747.pd