Resistance of the peptidyltransferase centre of rabbit ribosomes to attack by nucleases and proteinases.
Larger ribosomal subparticles (L-subparticles) of rabbit ribosomes were treated with either ribonucleases (I or T1) or proteinases (trypsin or chymotrypsin), and their capacity to function in poly(U)-directed polyphenylalanine synthesis and in the puromycin reaction was investigated. The effects of pretreatment of L-subparticles on the reconstruction of active subparticles from core-particles derived by treatment with 2.75 M-NH4Cl/69 mM-MgCl2 and split-protein fractions were also examined. The protein moiety of proteinase-treated L-subparticles was analysed by one-dimensional sodium dodecyl sulphate/polyacrylamide- and two-dimensional polyacrylamide-gel electrophoresis. The introduction of 16--100 scissions in the RNA moiety had no effect on the activity of the L-subparticles in polyphenylalanine synthesis, and there was no effect on the stability of L-subparticles to high-salt shock treatment and a marginal effect on the reconstruction of L-subparticles from high-salt-shock core-particles and split-protein fractions. In contrast, L-subparticles treated with low amounts of trypsin (0.56 ng of trypsin/microgram of L-subparticle) were inactive in polyphenylalanine synthesis, and their capacity to function in partial-reconstruction experiments was diminished. Activity in the puromycin reaction was increased by 70% as a result of trypsin treatment (280 ng of trypsin/microgram of L-subparticle). At least two of the acidic proteins implicated in the translocation function were not affected by trypsin treatment. Trypsin-treated L-subparticles had lost their capacity to bind the smaller ribosomal subparticle (S-subparticle). The protein(s) needed for S-subparticle binding were shown to be present in high-salt-shock cores. At least six proteins associated with the core-particles were attack during trypsin treatment of L-subparticles. An examination of L-subparticles isolated from trypsin-treated polyribosomes showed that the amount of trypsin necessary to decrease the activity of the subparticle by 50% was about twice that needed in the treatment of L-subparticles alone. The largest protein of rabbit L-subparticles (approx. 51 000 daltons) was cleaved in a stepwise fashion by trypsin to fragments of approx. 40 000 daltons. This protein was also cleaved by chymotrypsin.
D000217:Acyltransferases / Q000378:metabolism*; D000818:Animals; D002918:Chymotrypsin / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D066298:In Vitro Techniques; D010458:Peptidyl Transferases / Q000378:metabolism*; D010649:Phenylalanine / Q000096:biosynthesis; D011132:Polyribosomes / Q000187:drug effects / Q000201:enzymology; D011817:Rabbits; D006163:Ribonuclease T1 / Q000494:pharmacology; D012260:Ribonucleases / Q000494:pharmacology*; D012269:Ribosomal Proteins / Q000096:biosynthesis; D012270:Ribosomes / Q000187:drug effects / Q000201:enzymology*; D014357:Trypsin / Q000494:pharmacology*
D012269:Ribosomal Proteins; D010649:Phenylalanine; D000217:Acyltransferases; D010458:Peptidyl Transferases; D012260:Ribonucleases; D006163:Ribonuclease T1; D002918:Chymotrypsin; D014357:Trypsin