Biomaterial Database

Tim23p contains separate and distinct signals for targeting to mitochondria and insertion into the inner membrane. 1998

A J Davis, and K R Ryan, and R E Jensen

Department of Cell Biology and Anatomy, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.

The Tim23 protein is an essential inner membrane (IM) component of the yeast mitochondrial protein import pathway. Tim23p does not carry an amino-terminal presequence; therefore, the targeting information resides within the mature protein. Tim23p is anchored in the IM via four transmembrane segments and has two positively charged loops facing the matrix. To identify the import signal for Tim23p, we have constructed several altered versions of the Tim23 protein and examined their function and import in yeast cells, as well as their import into isolated mitochondria. We replaced the positively charged amino acids in one or both loops with alanine residues and found that the positive charges are not required for import into mitochondria, but at least one positively charged loop is required for insertion into the IM. Furthermore, we find that the signal to target Tim23p to mitochondria is carried in at least two of the hydrophobic transmembrane segments. Our results suggest that Tim23p contains separate import signals: hydrophobic segments for targeting Tim23p to mitochondria, and positively charged loops for insertion into the IM. We therefore propose that Tim23p is imported into mitochondria in at least two distinct steps.

UI	MeSH Term	Description	Entries
D007425	Intracellular Membranes	Thin structures that encapsulate subcellular structures or ORGANELLES in EUKARYOTIC CELLS. They include a variety of membranes associated with the CELL NUCLEUS; the MITOCHONDRIA; the GOLGI APPARATUS; the ENDOPLASMIC RETICULUM; LYSOSOMES; PLASTIDS; and VACUOLES.	Membranes, Intracellular,Intracellular Membrane,Membrane, Intracellular
D008565	Membrane Proteins	Proteins which are found in membranes including cellular and intracellular membranes. They consist of two types, peripheral and integral proteins. They include most membrane-associated enzymes, antigenic proteins, transport proteins, and drug, hormone, and lectin receptors.	Cell Membrane Protein,Cell Membrane Proteins,Cell Surface Protein,Cell Surface Proteins,Integral Membrane Proteins,Membrane-Associated Protein,Surface Protein,Surface Proteins,Integral Membrane Protein,Membrane Protein,Membrane-Associated Proteins,Membrane Associated Protein,Membrane Associated Proteins,Membrane Protein, Cell,Membrane Protein, Integral,Membrane Proteins, Integral,Protein, Cell Membrane,Protein, Cell Surface,Protein, Integral Membrane,Protein, Membrane,Protein, Membrane-Associated,Protein, Surface,Proteins, Cell Membrane,Proteins, Cell Surface,Proteins, Integral Membrane,Proteins, Membrane,Proteins, Membrane-Associated,Proteins, Surface,Surface Protein, Cell
D008928	Mitochondria	Semiautonomous, self-reproducing organelles that occur in the cytoplasm of all cells of most, but not all, eukaryotes. Each mitochondrion is surrounded by a double limiting membrane. The inner membrane is highly invaginated, and its projections are called cristae. Mitochondria are the sites of the reactions of oxidative phosphorylation, which result in the formation of ATP. They contain distinctive RIBOSOMES, transfer RNAs (RNA, TRANSFER); AMINO ACYL T RNA SYNTHETASES; and elongation and termination factors. Mitochondria depend upon genes within the nucleus of the cells in which they reside for many essential messenger RNAs (RNA, MESSENGER). Mitochondria are believed to have arisen from aerobic bacteria that established a symbiotic relationship with primitive protoeukaryotes. (King & Stansfield, A Dictionary of Genetics, 4th ed)	Mitochondrial Contraction,Mitochondrion,Contraction, Mitochondrial,Contractions, Mitochondrial,Mitochondrial Contractions
D002352	Carrier Proteins	Proteins that bind or transport specific substances in the blood, within the cell, or across cell membranes.	Binding Proteins,Carrier Protein,Transport Protein,Transport Proteins,Binding Protein,Protein, Carrier,Proteins, Carrier
D000090622	Mitochondrial Precursor Protein Import Complex Proteins	Multiprotein complexes that mediate import and sorting of mitochondrial preproteins into one of the four mitochondrial subcompartments: the outer membrane, the intermembrane space, the inner membrane, and the matrix. Mitochondrial protein import machinery includes translocase of the outer membrane (TOM) complex, translocases of the inner membrane (TIM) complex, beta‐barrel pathway complex, the mitochondrial intermembrane space import and assembly (MIA) pathway complex, carrier proteins of the inner membrane and the TIM23 complex and sorting and assembly machinery (SAM) complex.	MIA Complex,MIM Complex,Mitochondrial Import Complex,Mitochondrial Intermembrane Space Import and Assembly Complex,Mitochondrial Precursor Protein Import Machinery Proteins,Mitochondrial Preprotein Translocases,Mitochondrial Protein Import Machinery Proteins,SAM Complex,Sorting and Assembly Machinery Complex,TIM Complex,TIM23 Complex,TIMM Complex,TOM Channel,TOM Complex,TOM Translocase,TOMM Complex,TOMM Machinery,Translocase Outer Mitochondrial Membrane,Translocase of the Inner Membrane Complex,Translocase of the Inner Mitochondrial Membrane Complex,Translocase of the Outer Membrane Complex,Translocases of the Inner Membrane 23 Complex,Translocases of the Inner Membrane Complex,Import Complex, Mitochondrial,Preprotein Translocases, Mitochondrial,Translocase, TOM,Translocases, Mitochondrial Preprotein
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D001692	Biological Transport	The movement of materials (including biochemical substances and drugs) through a biological system at the cellular level. The transport can be across cell membranes and epithelial layers. It also can occur within intracellular compartments and extracellular compartments.	Transport, Biological,Biologic Transport,Transport, Biologic
D013329	Structure-Activity Relationship	The relationship between the chemical structure of a compound and its biological or pharmacological activity. Compounds are often classed together because they have structural characteristics in common including shape, size, stereochemical arrangement, and distribution of functional groups.	Relationship, Structure-Activity,Relationships, Structure-Activity,Structure Activity Relationship,Structure-Activity Relationships
D021382	Protein Sorting Signals	Amino acid sequences found in transported proteins that selectively guide the distribution of the proteins to specific cellular compartments.	Leader Signal Peptides,Leader Peptide,Leader Sequences, Peptide,Peptide Leader Sequences,Peptide Signal Sequences,Signal Peptide,Signal Peptides,Signal Sequence, Peptide,Signal Sequences,Signal Sequences, Peptide,Leader Peptides,Leader Sequence, Peptide,Leader Signal Peptide,Peptide Leader Sequence,Peptide Signal Sequence,Peptide, Leader,Peptide, Leader Signal,Peptide, Signal,Peptides, Leader,Peptides, Leader Signal,Peptides, Signal,Protein Sorting Signal,Sequence, Peptide Leader,Sequence, Peptide Signal,Sequence, Signal,Sequences, Peptide Leader,Sequences, Peptide Signal,Sequences, Signal,Signal Peptide, Leader,Signal Peptides, Leader,Signal Sequence,Signal, Protein Sorting,Signals, Protein Sorting,Sorting Signal, Protein,Sorting Signals, Protein
D026901	Membrane Transport Proteins	Membrane proteins whose primary function is to facilitate the transport of molecules across a biological membrane. Included in this broad category are proteins involved in active transport (BIOLOGICAL TRANSPORT, ACTIVE), facilitated transport and ION CHANNELS.	Biological Pump,Membrane Transport Protein,Membrane Transporter,Membrane Transporters,Metabolic Pump,Permease,Biological Pumps,Metabolic Pumps,Permeases,Pump, Biologic,Pump, Biological,Pump, Metabolic,Pumps, Biological,Pumps, Metabolic,Biologic Pump,Protein, Membrane Transport,Transport Protein, Membrane,Transport Proteins, Membrane,Transporter, Membrane,Transporters, Membrane