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Evidence that Axonal tRNAs Are Resistant to RNase and ATPase and Can Be Aminoacylated in the Absence of Exogenous ATP
Author(s) -
Chakraborty G.,
Nicola A.,
Ingoglia N. A.
Publication year - 1992
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1992.tb08901.x
Subject(s) - aminoacylation , rnase p , biochemistry , transfer rna , biology , axoplasm , atpase , enzyme , rna , axon , microbiology and biotechnology , gene
A high molecular weight (HMW) fraction of the 150,000 g supernatant of rat brain homogenates contains protein‐tRNA complexes which are able to incorporate [ 3 H]Arg and [ 3 H]Lys into tRNA. The aminoacylation of tRNA Arg was found to be dependent on ATP and inhibited by RNase. Conversely, the aminoacylation of tRNA Lys did not require exogenous ATP and was resistant to RNase and ATPase. In HMW fractions of regenerating rat sciatic nerves, the charging of both tRNA Arg and tRNA Lys was resistant to RNase and ATPase and did not require exogenous ATP. Because sciatic nerves are rich in axoplasm and tRNAs are known to be present in axons, we tested the hypothesis that degradative enzyme‐resistant, ATP‐tRNA complexes were of axonal origin. In HMW fractions from rat liver (containing no axons), both tRNA Arg and tRNA Lys were sensitive to RNase and required exogenous ATP for charging. But, in similar fractions of axoplasm obtained from the giant axon of squid, both tRNAs were insensitive to RNase and ATPase and did not require exogenous ATP for charging. These results suggest that tRNAs in axons are present in protected HMW complexes and contain endogenous stores of ATP. The presence of ATP in the HMW complexes was demonstrated by the luciferase‐luciferin assay for ATP. The nature of the protection of tRNAs from RNases was examined by dissociating proteins from HMW complexes by boiling, treating with proteinase K, or overho‐mogenizing the tissue. These procedures failed to render brain tRNA Lys susceptible to RNase. But phenol‐extracted, ethanol‐precipitated brain tRNA Lys was sensitive to RNase, suggesting that the protection of tRNA Lys may be by a protease‐ and heat‐resistant polypeptide or by a nonprotein‐aceous mechanism.