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The affinity of signal recognition particle for presecretory proteins is dependent on nascent chain length.
Author(s) -
Siegel V.,
Walter P.
Publication year - 1988
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1988.tb03007.x
Subject(s) - signal recognition particle , ribosome , biology , endoplasmic reticulum , signal recognition particle receptor , translation (biology) , signal peptide , biophysics , elongation , chromosomal translocation , biochemistry , protein targeting , transfer rna , protein biosynthesis , membrane , microbiology and biotechnology , peptide sequence , membrane protein , rna , messenger rna , gene , materials science , ultimate tensile strength , metallurgy
We have developed an assay in which incomplete preprolactin chains of varying lengths are targeted to the endoplasmic reticulum (ER) membrane in an elongation independent manner. The reaction had the same molecular requirements as nascent chain translocation across the ER membrane, namely, it was signal recognition particle (SRP) dependent, and required the nascent chain to be present as peptidyl tRNA (i.e. most likely ribosome associated) and to have its signal sequence exposed outside the ribosome. We found that the efficiency of the targeting reaction dropped dramatically as the chains grew longer than 140 amino acids in length, which probably reflected a decrease in affinity of the nascent chain‐ribosome complex for SRP. Thus at physiological SRP concentrations (10 nM) there appears a sharp cut‐off point in the ability of these chains to be targeted, while at high SRP concentrations (270 nM) all chains could be targeted. In kinetic experiments, high concentrations of SRP were found to change the time in elongation after which translocation of the nascent polypeptide could no longer occur.