A fast dynamic mode of the EF‐G‐bound ribosome

A key intermediate in translocation is an ‘unlocked state’ of the pre‐translocation ribosome in which the P‐site tRNA adopts the P/E hybrid state, the L1 stalk domain closes and ribosomal subunits adopt a ratcheted configuration. Here, through two‐ and three‐colour smFRET imaging from multiple structural perspectives, EF‐G is shown to accelerate structural and kinetic pathways in the ribosome, leading to this transition. The EF‐G‐bound ribosome remains highly dynamic in nature, wherein, the unlocked state is transiently and reversibly formed. The P/E hybrid state is energetically favoured, but exchange with the classical P/P configuration persists; the L1 stalk adopts a fast dynamic mode characterized by rapid cycles of closure and opening. These data support a model in which P/E hybrid state formation, L1 stalk closure and subunit ratcheting are loosely coupled, independent processes that must converge to achieve the unlocked state. The highly dynamic nature of these motions, and their sensitivity to conformational and compositional changes in the ribosome, suggests that regulating the formation of this intermediate may present an effective avenue for translational control.     

The quantification of formazans in tissue sections by microdensitometry. I. The use of neotetrazolium chloride

Synopsis This article describes the use of a microdensitometer for the measurement of formazan deposits in tissue sections. Some examples are given to illustrate the various applications of this technique in the assessment of glucose-6-phosphate dehydrogenase activity. These are (1) the separate measurement of the red half-formazan intermediate and purple diformazan of neotetrazolium, and the effect of incubation time on their production, (2) the measurement of activities in different regions of the liver lobule, and the selective effect of phenobarbitone, and (3) the measurement of enzyme activity in individual cartilage cells in normal and osteoarthrosis-prone animals. All activities can be expressed in absolute units as nmol hydrogen/mm³/hr, and thus compared with standard biochemical data. The activities obtained all fall within the range of published values for biochemical systems.Paper given at the Royal Microscopical Society's European Histochemistry Meeting at Nottingham in September 1975.     

An endonuclease from Chlamydomonas reinhardtii that cleaves the sequence TATA

An endodeoxyribonuclease, designated CreI, was purified 16,000-fold from zygotes of the eukaryote Chlamydomonas reinhardtii. CreI preferentially attacks the sequence TATA producing double strand breaks with 3'-phosphomonoester and 5'-hydroxyl termini. The endonuclease has an Mr = 27,000 and requires Ca2+ at pH 7.5 for optimal activity.     

Identification of Tumor Antigens in the HLA Peptidome of Patient-derived Xenograft Tumors in Mouse

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Highlights

• •Sufficient tumor tissues are often unavailable large HLA peptidome discovery.
• •Using patient derived xenograft (PDX) tumors can overcome this limitation.
• •The large PDX HLA peptidomes expand significantly those of the original biopsies.
• •The HLA peptidomes of the PDX tumors included many tumor antigens.