ISSN:
1573-4919
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Summary Once formylated, eukaryotic initiator tRNA behaves in anE. coli translation system like the homologous initiator, in its binding to ribosomes and ability to form a peptide bond with puromycin. Conversely, anE. coli initiator tRNA, either formylated or not, can bind to reticulocyte ribosomes in the presence of poly AUG and reticulocyte factors, but no transfer to puromycin is obtained. Thus, eukaryotic ribosomes seem to impose a more stringent discrimination as far as the biological specificity of initiator tRNA is concerned than doE. coli ribosomes. The possibility to interchange initiation factors has also been examined. When added to reticulocyte 40S subunits,E. coli initiation factors catalyze poly AUG dependent binding ofE. coli initiator tRNA whether formylated or not. Thus, ability ofE. coli factors to discriminate between the N-formyl substituted and unformylated initiator is lost when the ribosomal context is modified. Also in support to the role of the ribosome in tRNA selection is the fact that eukaryotic tRNA's which are recognized by a completeE. coli ribosomal system fail to react whenE. coli factors are crossed with reticulocyte ribosomes. Reticulocyte IF prepared by 2 hrs KCl extraction from ribosomes (IF2hrs) shows no catalytic activity onE. coli ribosomes whereas IF prepared by shorter KCl extraction (IF1/2hr) stimulates low but appreciableE. coli or reticulocyte fMet-tRNA binding to 70S ribosomes. A similar activity is displayed by partially purified IF-M1. Both IF1/2hr and IF-M1 dependent binding to heterologous ribosomes readily take place in the absence of GTP and no transfer to puromycin is observed. Complementation betweenE. coli IF1 and reticulocyte IF-M1 for fMet-tRNA binding to reticulocyte 40S subunits has been obtained suggesting functional similarities between IF-M1 andE. coli IF2. The possible role of IF-M1 in the homologous reaction is discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01659939
Permalink