From the thermoacidophilic archaebacterium, Thermopiasma acidophilum, a proteolytically active particle has been isolated which is almost identical in size. and shape with the multicatalytic proteinase (prosome) from rat. This result indicates that prosomes have been developed early in evolution and that they possibly serve functions common to all living cells.

All eukaryotic cells so far analysed contain 19S particles which share a cylinder-like shape and are composed of a set of proteins of relative molecular mass ranging typically from 19,000 to 36,000 (refs 1-10). Proposed functions have included synthetase activity, transfer RNA processing or messenger RNA repression, but their biological importance remains obscure. A multicatalytic proteinase (MCP) of similar size and shape has been isolated from mammalian tissues. The apparent similarities of these high molecular weight complexes suggest a biochemical and functional homology between the small cytoplasmic 19S particle from Drosophila melanogaster (19S-scRNP) (ref. 7) and rat MCP (ref. 14). By means of electron microscopy, immunological techniques, RNA identification and proteinase activity assays, we were able to show that the two structurally similar complexes are immunologically related ribonucleoproteins (RNPs) with similar proteolytic activity.

On electron micrographs, negatively stained multicatalytic proteinase molecules are viewed end-on (ring shaped) or sideon (rectangular shaped). For aurothioglucose, ammonium molybdate-and phosphotungstate-stained molecules, the dimensions measured are consistent. In contrast, uranyl acetate-staining reveals ring-shaped particles which vary in diameter between 12 and 16 nm. This is due to a partial collapse and substantial flattening of the structure. Digital image analysis of side-on views of the particles reveals a tripartite, reel-shaped structure. Within the ring-like, end-on projections of ammonium molybdate-stained molecules six local centres of mass can be discerned; their position appears to depart, however, from a true six-fold symmetry.

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In human 20S proteasomes two copies of each of seven different ␣-type and seven different ␤-type subunits are assembled to form a stack of four sevenmembered rings, giving the general structure ␣ 1-7 , ␤ 1-7 , ␤ 1-7 , ␣ 1-7 . By means of immunoelectron microscopy and chemical crosslinking of neighboring subunits, we have determined the positions of the individual subunits in the proteasome. The topography shows that for the trypsin-like, the chymotrypsin-like, and the postglutamyl cleaving activities, the pairs of ␤ type subunits, which are thought to form active sites, are nearest neighbors.

Two methods for the estimation of the turbulence energy dissipation rate (TEDR) from data measured by a 2-μm coherent Doppler lidar are described in this paper. Based on data measured at the Tarbes-Lourdes-Pyrénées International Airport in summer 2003, height profiles of TEDR have been retrieved. The results of TEDR estimation both from the Doppler spectrum width and from the velocity structure function are compared. Moreover, the experiment has been treated by numerical simulation and the theoretical results have been used for verification of the described methods.

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The subunit topography of the Thermoplasma acidophilum proteasome was determined by immunoelectron microscopy using monospecific antibodies directed against the two constituent subunits (,v~). Anti-at-subunit lgG was found to bind to the outer disks of the cylinder-or barrel.shaped molecule, while the binding sites of the anti-fl-subunit lgG were mapped on the two inner rings. Probably the homologues of the two subunits in the compositionally more complex but isomorphous eukaryotie proteasomes occupy equivalent positions.Proteasome; Multicatalytic proteinase; Archaebacterium: lmmunoelcctron microscopy