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The N-terminal domain of Tim23, a key component of the mitochondrial preprotein translocase, is now known to be exposed on the surface of the outer mitochondrial membrane. The spanning of two membranes on the part of Tim 23 is novel in membrane biology.

Tim22 is responsible for the import of proteins belonging to the mitochondrial ADP/ATP carrier (AAC) into the inner membrane. Tim22 is present in an assembly of high relative molecular mass, which is different from the Tim23-Tim17 complex and is present in the inner membrane of the mitochondria. Import of the AAC family proteins are independent of Tim23 but is dependent on the Tim22. The import of the preproteins having matrix targeting signals is independent of Tim22. This indicates that Tim22 represents a pathway distinct and independent of Tim23 pathway.

Membrane potential promotes the formation of dimers that display dynamic behavior by Tim23, an important component of the protein import machinery of the mitochondria's inner membrane. In turn, dimer dissociation is triggered when a matrix targeting sequence binds to Tim23. These all show that Tim23 significantly influences protein import.

Two new proteins MIM33 and MIM14 are components of the mitochondrial inner membrane (MIM) besides two known proteins MIM23 and MIM17 which also form a part of the complex. The import of nuclear mitochondrial preproteins takes place in a coordinated manner across the mitochondrial membrane. Translocation systems in both the outer and inner membranes take part in the process. The MIM complex can accept preproteins and cause reversible transmembrane movement with mitochondrial outer membrane and unidirectional transport through linkage with the ATP-dependent mt-Hsp70-MIM44 system.

The mitochondrial complex Hsp70/MIM44 enhances protein vectorial translocation in mitochondrial membranes by sequential interaction. Synthesis of the Hsp70/MIM44 complex depends on the hydrolysis of adenosine triphosphate. Hsp70 is a mitochondrial protein essential for protein translocation into the mitochondria, and the protein incorporating devices of the mitochondria acquire Hsp70 as Hsp70/MIM44 by the interaction of MIM44, a mitochondrial inner membrane component, with the Hsp70 of the mitochondrial matrix.

The Rhesus antigen Ew (ISBT designation 004 011) was first described in 1955. It is defined by a specific antibody, but its molecular genetic basis has not yet been resolved. Two individuals serologically characterized to express the rare Rhesus antigen Ew were analyzed by sequencing of all 10 exons of the RHCE gene. A nucleotide exchange at position 500 (T500A) resulting in a Met167Lys amino acid substitution was found in both individuals. Moreover, we show that an individual carrying the Ew antigen is capable to produce an alloantibody against the wild-type E antigen. The single-point mutation T500A in exon 4 of the RHCE gene is a molecular basis of the rare Rhesus antigen Ew. [ABSTRACT FROM AUTHOR]

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