Biomedical subjects

K Abu-Elneel

Publications and source records attributed to K Abu-Elneel.

3 recordsLinked to original sources

PubMed2001

Intramitochondrial localization of universal minicircle sequence-binding protein, a trypanosomatid protein that binds kinetoplast minicircle replication origins.

Kinetoplast DNA (kDNA), the mitochondrial DNA of the trypanosomatid Crithidia fasciculata, is a unique structure containing 5,000 DNA minicircles topologically linked into a massive network. In vivo, the network is condensed into a disk-shaped structure. Replication of minicircles initiates at unique origins that are bound by universal minicircle sequence (UMS)-binding protein (UMSBP), a sequence-specific DNA-binding protein. This protein, encoded by a nuclear gene, localizes within the cell's single mitochondrion. Using immunofluorescence, we found that UMSBP localizes exclusively to two neighboring sites adjacent to the face of the kDNA disk nearest the cell's flagellum. This site is distinct from the two antipodal positions at the perimeter of the disk that is occupied by DNA polymerase beta, topoisomerase II, and a structure-specific endonuclease. Although we found constant steady-state levels of UMSBP mRNA and protein and a constant rate of UMSBP synthesis throughout the cell cycle, immunofluorescence indicated that UMSBP localization within the kinetoplast is not static. The intramitochondrial localization of UMSBP and other kDNA replication enzymes significantly clarifies our understanding of the process of kDNA replication.

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PubMed1999

Universal minicircle sequence-binding protein, a sequence-specific DNA-binding protein that recognizes the two replication origins of the kinetoplast DNA minicircle.

Replication of the kinetoplast DNA minicircle lagging (heavy (H))-strand initiates at, or near, a unique hexameric sequence (5'-ACGCCC-3') that is conserved in the minicircles of trypanosomatid species. A protein from the trypanosomatid Crithidia fasciculata binds specifically a 14-mer sequence, consisting of the complementary strand hexamer and eight flanking nucleotides at the H-strand replication origin. This protein was identified as the previously described universal minicircle sequence (UMS)-binding protein (UMSBP) (Tzfati, Y., Abeliovich, H., Avrahami, D., and Shlomai, J. (1995) J. Biol. Chem. 270, 21339-21345). This CCHC-type zinc finger protein binds the single-stranded form of both the 12-mer (UMS) and 14-mer sequences, at the replication origins of the minicircle L-strand and H-strand, respectively. The attribution of the two different DNA binding activities to the same protein relies on their co-purification from C. fasciculata cell extracts and on the high affinity of recombinant UMSBP to the two origin-associated sequences. Both the conserved H-strand hexamer and its flanking nucleotides at the replication origin are required for binding. Neither the hexameric sequence per se nor this sequence flanked by different sequences could support the generation of specific nucleoprotein complexes. Stoichiometry analysis indicates that each UMSBP molecule binds either of the two origin-associated sequences in the nucleoprotein complex but not both simultaneously.

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PubMed1996

Dictyostelium myosin II is regulated during chemotaxis by a novel protein kinase C.

The myosin II heavy chain (MHC)-specific protein kinase C (MHC-PKC) isolated from Dictyostelium discoideum has been implicated in the regulation of myosin II assembly in response to the chemoattractant, cAMP (Ravid, S., and Spudich, J. A. (1989) J. Biol. Chem. 264, 15144-15150). Here we report that elimination of MHC-PKC results in the abolishment of MHC phosphorylation in response to cAMP. Cells devoid of MHC-PKC exhibit substantial myosin II overassembly, as well as aberrant cell polarization, chemotaxis, and morphological differentiation. Cells overexpressing the MHC-PKC contain highly phosphorylated MHC and exhibit impaired myosin II localization and no apparent cell polarization and chemotaxis. The results presented here provide direct evidence that MHC-PKC phosphorylates MHC in response to cAMP and plays an important role in the regulation of myosin II localization during chemotaxis.

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