The f luorescence decay functions of individual, specifically labeled tRNA Phe molecules exhibit nonexponential character as a result of conformational dynamics occurring during the measurement on a single molecule. tRNA Phe conformational states that interchange much more slowly are evidenced by the distribution of lifetimes observed for many individual molecules. A structural model for the nonexponential decay indicates that the tRNA Phe -probe adduct f luctuates between two states, one of which provides conditions that quench the probe f luorescence.

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The ribosome is universally responsible for synthesizing proteins by translating the genetic code transcribed in mRNA into an amino acid sequence. Ribosomes use cellular accessory proteins, soluble transfer RNAs, and metabolic energy to accomplish the initiation, elongation, and termination of peptide synthesis. In translocating processively along the mRNA template during the elongation cycle, ribosomes act as supramolecular motors. Here we demonstrate that ribosomes adsorbed on a surface, as for mechanical or spectroscopic studies, are capable of polypeptide synthesis and that tethered particle analysis of fluorescent beads connected to ribosomes via polyuridylic acid can be used to estimate the rate of polyphenylalanine synthesis by individual ribosomes. This work opens the way for application of biophysical techniques, originally developed for the classical motor proteins, to the understanding of protein biosynthesis.

Reverse-phase HPLC was used to fractionate 40s ribosomal proteins from human placenta. Application of a C, reverse-phase column allowed us to obtain 27 well-resolved peaks. The protein composition of each chromatographic fraction was established by two-dimensional polyacrylamide gel electrophoresis and N-terminal sequencing. N-terminally blocked proteins were cleaved with endoproteinase Lys-C, and suitable peptides were sequenced. All sequences were compared with those of ribosomal proteins available from data bases. This allowed us to identify all proteins from the 40s human ribosomal subunit in the HPLC elution profile. By matrix-assisted laser-desorption ionization mass spectrometry the masses of the 40s proteins were determined and checked for the presence of post-translational modifications. For several proteins differences to the deduced sequences and the calculated masses were found to be due to post-translational modifications.Keywords: human ribosomal proteins ; HPLC ; N-terminal and internal amino acid sequencing ; matrixassisted-laser-desorption ionization MS ; post-translational modifications.Human ribosornd proteins are the main components of the fundamental processes which translate genetic information into proteins at the ribosome. Some ribosomal proteins (rp) are further involved in non-ribosomal functions. Recently, rp L7 was shown to contain the basic-region-leucine-zipper sequence which mediates the stable binding of this protein to DNA [I]. Moreover, rp S3 was found to act as an endonuclease in the DNA-repairing system [2]. Finally, some data indicate that tumor diseases may be accompanied by overexpression of rp genes 13, 4) and by chromosomal rearrangements in regions of rp genes [ S ] . Therefore, structural analysis of these proteins is necessary for complete understanding of their fundamental role in the cell. The task of structure determination of rat rp has been almost fully resolved by the application of recombinant-DNA technology ; details are reviewed in [6]. However, knowledge of the cDNA sequences does not provide information concerning post-translational modifications of the proteins after their biosynthesis and assembly into the ribosomal subunits. Several modifications of rp have been determined in the eubacterial ribosome [7, 81, and the eukaryotic rprotein S6 is known to be phosphorylated 191. This phosphorylation was shown to be connected with cell growth [I 01 and cell cycle control [I I]. At least seven 40s proteins from HeLa cells were found to be methylated, and the level of their methylation was shown to be altered in the Abbreviations. MALDI, matrix-assisted laser-desorption ionization ; Lys-C, endoproteinase Lys-C; RP, reverse-phase; rp, ribosomal protein ; S-proteins, proteins of the small ribosomal subunit; 40S, small ribosomal subunit; TP40, total protein mixture of the small ribosomal subunit; TOF, time-of-flight ; Pth-Xaa, phenylthiohydantoin -amino-acid.course of the cell cycle [12]. It is also known that ribosomal proteins may be acetylated 17, 13, 141. However...

The 60S ribosomal proteins were isolated from ribosomes of human placenta and separated by reversed phase HPLC. The fractions obtained were subjected to trypsin and Glu-C digestion and analyzed by mass fingerprinting (MALDI-TOF), MS/MS (ESI), and Edman sequencing. Forty-six large subunit proteins were found, 22 of which showed masses in accordance with the SwissProt database (June 2002) masses (proteins L6, L7, L9, L13, L15, L17, L18, L21, L22, L24, L26, L27, L30, L32, L34, L35, L36, L37, L37A, L38, L39, L41). Eleven (proteins L7, L10A, L11, L12, L13A, L23, L23A, L27A, L28, L29, and P0) resulted in mass changes that are consistent with N-terminal loss of methionine, acetylation, internal methylation, or hydroxylation. A loss of methionine without acetylation was found for protein L8 and L17. For nine proteins (L3, L4, L5, L7A, L10, L14, L19, L31, and L40), the molecular masses could not be determined. Proteins P1 and protein L3-like were not identified by the methods applied.

The 23S rRNA nucleotides 2604-12 and 2448-58 fall within the central loop of domain V, which forms a major part of the peptidyl transferase center of the ribosome. We report the synthesis of radioactive, photolabile 2'-O-methyloligoRNAs, PHONTs 1 and 2, complementary to these nucleotides and their exploitation in identifying 50S ribosomal subunit components neighboring their target sites. Photolysis of the 50S complex with PHONT 1, complementary to nts 2604-12, leads to target site-specific photoincorporation into protein L2 and 23S rRNA nucleotides A886, Alpha1918, A1919, G1922-C1924, U2563, U2586, and C2601. Photolysis of the 50S complex with PHONT 2, complementary to nts 2448-58, leads to target site-specific probe photoincorporation into proteins L2, L3, one or more of proteins L17, L18, L21, and of proteins L9, L15, L16, and 23S rRNA nucleotides C2456 and psi2457. Chemical footprinting studies show that 2'-O-methyloligoRNA binding causes little distortion of the peptidyl transferase center but do provide suggestive evidence for the location of flexible regions within 23S rRNA. The significance of these results for the structure of the peptidyl transferase center is considered.

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