Large Subunit

Different projections of the bacterial 50S subunit and its crude model is shown in Fig. 5.8. This subunit is more isometric than the small one, the linear size being equal to 200 to 230 A in all directions. Three peripheral protuberance can be distinguished: the central one (CP) may be termed the head; the lateral finger-like protuberance is called the L7/L12 stalk; and still another lateral protuberance, located on the other side of the central protuberance, is referred to as the side lobe or L1 ridge (in the case of E. coli 50S ribosomal subunit, the two lateral protuberances contain ribosomal proteins L7/L12 and L1, respectively;

Figure 5.7. Averaged images of negatively stained 30S (upper row) and 40S (lower row) ribosomal subunits in the same three projections as shown in Figs. 5.5 and 5.6. (Original photos by V.D. Vasiliev).

see Section 7 for more details).

Averaged images of the large ribosomal subunit of E. coli (Fig. 5.9) make all details traceable in individual particle images clearly revealed. Again, the deep groove is seen to separate the head (CP) from the remainder of the subunit, the groove being deeper on the side of the L1 ridge than on the side of the L7/L12 stalk. One can see that the body of the subunit is bifurcated on the side opposite the head. In addition, the averaged images demonstrated that many of the smaller details are not random features but are reproducible in numerous images. The eukaryotic 60S subunit has all the same main morphological features.

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