70S ribosome

What could be the signal for the induction of the cold shock proteins It has been observed that shifting E. coli cells from 37 to 5 °C results in an accumulation of 70S monosomes with a concomitant decrease in the number of polysomes [129]. Further, it has been shown that a cold shock response is induced when ribosomal function is inhibited, e.g. by cold-sensitive ribosomal mutations [121] or by certain antibiotics such as chloramphenicol [94]. These data indicate that the physiological signal for the induction of the cold shock response is inhibition of translation caused by the abrupt shift to lower temperature. Then, the cold shock proteins RbfA, CsdA and IF2 associate with the 70S ribosomes to convert the cold-sensitive nontranslatable ribosomes into cold-resistant translatable ribosomes. This in turn results in an increase in cellular protein synthesis and growth of the cells. 

The atomic structure of this subunit and its complexes with substrate analogs revealed the enzymatic activity of the rRNA backbone. Thus, the ribosome is in fact a ribozyme P Nissen, J Hansen, N Ban, PB Moore, TA Steitz. Science 289 920-930, 2000. Atomic structure of the ribosome s small 30S subunit, resolved at 5 A WM Clemons Jr, JL May, BT Wimberly, JP McCutcheon, MS Capel, V Ramakrishnan. Nature 400 833-840, 1999. The 8-A crystal structure of the 70S ribosome reveals a double-helical RNA bridge between the 50S and the 30S subunit GM Culver, JH Cate, GZ Yusupova, MM Yusupov, HF Noller. Science 285 2133-2136, 1999. 

Skold, S.-E. (1983) Chemical crosslinking of elongation factor G to the 23S RNA in 70S ribosomes from Escherichia coli. Nucleic Acids Res. 11, 4923. 

Once the amino acid has been bound to its tRNA, it can pass to the next phase of protein synthesis, involving its interaction with mRNA, which takes place on the ribosome, a molecular machine of enormous complexity. The ribosome of E. coli is a ribonucleoprotein assembly of molecular weight 2700 kDa, and sedimentation constant of 70S9. It is made up of roughly two-thirds RNA and one-third protein, and can be separated into a small (30S) and a large (50S) subunit. The 30S subunit contains 21 proteins and one 16S RNA molecule, while the large subunit has 34 different proteins and two RNA molecules, one 23S and one 5S. Despite its size and complexity, the structure of both ribosomal subunits has been determined to atomic resolution (Figure 4.32), and very recently the atomic structure of the 70S ribosome has been determined at 2.8 A resolution (Selmer et al., 2006). 

Figure 4.32 A space-filling model of the 70S ribosome the three RNA molecules—5S, 16S and 23 S—are in white, yellow and purple, respectively ribosomal proteins of the large and small subunit are in blue and green, respectively the tRNA in the A-site, with its 3 -end extending into the peptidyl-transferase cavity is in red and the P-site tRNA is in yellow. (From Moore and Steitz, 2005. Copyright (2005) with permission from Elsevier.)...

Sedimentation coefficients are expressed in Svedbergs (S), after the Swedish biochemist The Svedberg who developed the ultracentrifuge in the 1920s. While S values are indicative of molecular weight, they are not addi-tive-the 70s ribosome is made up of one 50S and one 30S subunit. 

A nasopharyngeal swab obtained from a 4-month-old infrint with rhinitis and paroxysmal coughing tested positive upon culture for Bordetella pertussis. He was admitted to the hospital for therapy with an antibiotic that inhibits the translocation of peptidyl-tRNA on 70S ribosomes, This patient was most likely treated with... 

S small subunit ribosomal RNA Small subunit of the 70S ribosome of... 

Our first microcrystals were of Bacillus stearothermophilus SOS subunits and of 70S ribosomes from E. coli they were mainly grown from lower alcohols, toluene, or chloroform. Each ribosomal preparation required slightly different crystallization conditions, and often the preparation had almost been exhausted by the time conditions were optimised. We also found that crystals grew from active particles only. 

Gabashvili IS, Agrawal RK, Grassucci R, Squires CL, Dahlberg AE, Frank J (1999) Major rearrangements in the 70S ribosomal 3D structure caused by a conformational switch in 16S ribosomal RNA. EMBO J 18 6501-6507... 

The selection of transformed chloroplasts usually involves the use of an antibiotic resistance marker. Spectinomycin is used most routinely because of the high specificity it displays as a prokaryotic translational inhibitor as well as the relatively low side effects it exerts on plants. The bacterial aminoglycoside 3 -adenyltransferase gene (ciadA) confers resistance to both streptomycin and spectinomycin. The aadA protein catalyzes the covalent transfer of an adenosine monophosphate (AMP) residue from adenosine triphosphate (ATP) to spectinomycin, thereby converting the antibiotic into an inactive form that no longer inhibits protein synthesis for prokaryotic 70S ribosomes that are present in the chloroplast. 

Linezolid s a novel oxazolidinone antibiotic with exclusively Gram-positive activity (including MRSA) which acts at the level of the 30S and 70S ribosomal subunits by a unique mechanism it inhibits protein synthesis by preventing formation of initiation complexes. Linezolid has excellent oral bioavailability and tissue penetration the most important adverse effect is marrow suppression which is usually reversible. Its major indications are soft tissue infections and nosocomial pneumonia, although these will probably expand in the future. 

All ribosomes have two subunits, and each subunit contains several protein chains and one or more chains of RNA (ribosomal RNA, or rRNA). In the ribosome from E. coli, the smaller of the two subunits is known as the 30S subunit and the larger is referred to as the 50S subunit. (The unit S stands for Svedberg, a measure of how rapidly a particle sediments in a centrifuge.) The two subunits combine to form the active 70S ribosomal assembly. The special RNA molecules that are a part of the ribosome are quite distinct from messenger or transfer RNA molecules, and they play important roles in forming the overall ribosomal quaternary structure and in aligning mRNA and tRNA molecules during protein biosynthesis. 

Using a tubular-bowl centrifuge, calculate the sedimentation velocity of a 70S ribosome (from E. coli, diameter 0.02 pm) in water at 20 °C. The rotational speed and distance from the center are 30 000 rpm and 10 cm, respectively. 

How many times g should the centrifugal force be in order to obtain a 10-fold higher sedimentation velocity of a 70S ribosome than that obtained in Example 9.2 ... 

Functional 70S ribosome (initiation complex) Aminoacyl-tRNAs specified by codons Elongation factors (EF-Tu, EF-Ts, EF-G)... 

Protein synthesis occurs on the ribosomes, which consist of protein and rRNA. Bacteria have 70S ribosomes, with a large (SOS) and a small (30S) subunit. Eukaryotic ribosomes are significantly larger (80S) and contain more proteins. 

Figure 29-1 (A-C) A 1970s view of a bacterial ribosome achieved by electron microscopy and image reconstruction. These interface views show the surfaces that face each other in the 70S ribosome.

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