Title
Identification of cytoplasmic residues of Sec61p involved in ribosome binding and cotranslational translocation
GSBS Program
Biochemistry & Molecular Pharmacology
UMMS Affiliation
Graduate School of Biomedical Sciences; Department of Biochemistry and Molecular Pharmacology
Date
1-6-2005
Document Type
Article
Medical Subject Headings
Amino Acid Sequence; Animals; Biological Transport; Humans; Liposomes; Membrane Proteins; Models, Molecular; Molecular Sequence Data; Phenotype; Point Mutation; Protein Binding; *Protein Biosynthesis; Protein Precursors; Protein Structure, Secondary; Ribosomes; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Sequence Alignment
Disciplines
Life Sciences | Medicine and Health Sciences
Abstract
The cytoplasmic surface of Sec61p is the binding site for the ribosome and has been proposed to interact with the signal recognition particle receptor during targeting of the ribosome nascent chain complex to the translocation channel. Point mutations in cytoplasmic loops six (L6) and eight (L8) of yeast Sec61p cause reductions in growth rates and defects in the translocation of nascent polypeptides that use the cotranslational translocation pathway. Sec61 heterotrimers isolated from the L8 sec61 mutants have a greatly reduced affinity for 80S ribosomes. Cytoplasmic accumulation of protein precursors demonstrates that the initial contact between the large ribosomal subunit and the Sec61 complex is important for efficient insertion of a nascent polypeptide into the translocation pore. In contrast, point mutations in L6 of Sec61p inhibit cotranslational translocation without significantly reducing the ribosome-binding activity, indicating that the L6 and L8 sec61 mutants affect different steps in the cotranslational translocation pathway.
Rights and Permissions
Citation: J Cell Biol. 2005 Jan 3;168(1):67-77. Link to article on publisher's site