Reassociation of dissociated structural protein with ribosomal particles of an extremely halophilic bacterium

In vitro reassembly of active large ribosomal subunits of the halophilic archaebacterium Haloferax mediterranei

The large ribosomal subunits of the halophilic archaebacterium Haloferax mediterranei have been reconstituted in vitro from the dissociated RNA and protein components. Efficient reassembly of particles fully active in poly(U)-directed polyphenylalanine synthesis requires a 2-h incubation at 42 degrees C in the presence of no less than 2.5 M concentrations of monovalent cations and of 60 mM magnesium. K+ and NH4+ ions are equally effective in promoting subunit reconstitution; however, maximal efficiency is attained when they are combined in a 1:2 molar ratio. The reassembly process requires no heat activation step, as under the appropriate ionic conditions it takes place spontaneously within the temperature range optimal for growth of H. mediterranei cells (40-45 degrees C).

Lack of detectable polyamines in an extremely halophilic bacterium

Polyamines (putrescine, spermidine, spermine and other analogs) were not detectable by the dansylation procedure coupled with HPLC analysis in an extremely halophilic bacterium, Halobacterium halobium. Based on the detection limit of this analytical method, we estimated that the polyamine content in H. halobium, if present, was less than 0.06% of that of E. coli. Putrescine uptake and the metabolic conversion of ornithine or arginine to polyamines were negligible in this bacterium. In a H. halobium cell-free extract, a saturated amount of KC1 was needed for poly(U) directed polyphenylalanine synthesis; neither putrescine nor spermidine could replace KC1. These results suggest that polyamines may play an insignificant role in the growth of this halophilic bacterium.

Self-assembly of biological structures

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Ribosomes: effect of interferon on their interaction with rapidly labeled cellular and viral RNA's

Rapidly labeled RNA of mouse L cells and labeled RNA of Mengo virus, unlike cellular RNA labeled under steady-state conditions, form detectable complexes with L-cell ribosomes. These ribosome-RNA complexes formed in vitro appear analogous to those assembled during polysome formation in vivo. When ribosomes are prepared from L cells exposed to homologous interferon, their capacity to associate with cell messenger is preserved, while their ability to interact with viral RNA is markedly reduced. The ribosomes from cells exposed to interferon are thus altered selectively to permit only certain messages to be bound and translated.