LepA exhibits uncoupled GTPase activity. This activity is stimulated by the ribosome to the same extent as the activity of EF-G, which is known to have the strongest ribosome-dependent GTPase activity among all characterized G proteins involved in translation. Conversely, uncoupled GTPase activity occurs when the ribosome stimulation of GTP cleavage is not directly dependent on protein synthesis. In the presence of GTP, LepA works catalytically. On the other hand, in the presence of the nonhydrolysable GTP – GDPNP – the LepA action becomes stoichiometric, saturating at about one molecule per 70S ribosomes. This data demonstrates that GTP cleavage is required for dissociation of LepA from the ribosome, which is demonstrative of a typical G protein. At low concentrations of LepA (less than or equal to 3 molecules per 70S ribosome), LepA specifically recognizes incorrectly translocated ribsosomes, back-translocates them, and thus allows EF-G to have a second chance to catalyze the correct translocation reaction. At high concentrations (about 1 molecule per 70S ribosome), LepA loses its specificity and back-translocates every POST ribosome. This places the translational machinery in a nonreproductive mode. This explains the toxicity of LepA when it is found in a cell in high concentrations. Hence, at low concentrations LepA significantly improves the yield and activity of synthesized proteins; however, at high concentrations LepA is toxic to cells.
Additionally, LepA has an effect on peptide bond formation. Through various studies in which functional derivatives of ribosomes were mixed with puromycin (an analog of the 3' end of an aa-tRNA) it was determined that adding LepA to a post transcriptionally modified ribosome prevents dipeptide formation as it inhibits the binding of aa-tRNA to the A site.
Read more about this topic: Leader Peptidase A
Other articles related to "activity":
... that "the prime minister directs and coordinates the activity of the ministers" ... Often the prime minister's activity consists more in mediating between the various parties in the majority coalition, rather than directing the activity of the Council of ...
... for a very intense fishing and sea-trading activity ... centre, in contrast with Vigo, which attracted the industrial activity ... Industrial activity is reduced to a handful of companies, namely pulp mills (in gradual recession) and construction ...
... two identical "heavy chains," 520 kDa in mass, which contain the ATPase activity and are thus responsible for generating movement along the microtubule two 74 kDa intermediate ... The force-generating ATPase activity of each dynein heavy chain is located in its large doughnut-shaped "head", which is related to other AAA proteins, while two projections from the head connect it to other ... The alternating activity of the paired heavy chains in the complete cytoplasmic dynein motor enables a single dynein molecule to transport its cargo by "walking" a ...
... A warm-up generally consists of a gradual increase in intensity in physical activity (pulse raiser), a joint mobility exercise, stretching and a sport ... energy systems that are required for that particular activity ...
... effusive and extrusive dacitic and rhyolitic activity ... Almost all of its eruptions involved phreatic activity ... The latest eruptive activity was a steam explosion in 1888, after small ash eruptions in 1871 and 1873 and earthquakes are not infrequent ...
Famous quotes containing the word activity:
“Amour is the one human activity of any importance in which laughter and pleasure preponderate, if ever so slightly, over misery and pain.”
—Aldous Huxley (18941963)
“In communist society, where nobody has one exclusive sphere of activity but each can become accomplished in any branch he wishes, society regulates the general production and thus makes it possible for me to do one thing today and another tomorrow, to hunt in the morning, fish in the afternoon, rear cattle in the evening, criticize after dinner, just as I have a mind, without ever becoming hunter, fisherman, shepherd or critic.”
—Karl Marx (18181883)
“The Good of man is the active exercise of his souls faculties in conformity with excellence or virtue.... Moreover this activity must occupy a complete lifetime; for one swallow does not make spring, nor does one fine day; and similarly one day or a brief period of happiness does not make a man supremely blessed and happy.”
—Aristotle (384322 B.C.)