Biomedical subjects

S Heidmann

Publications and source records attributed to S Heidmann.

13 recordsLinked to original sources

PubMed2001

Drosophila separase is required for sister chromatid separation and binds to PIM and THR.

Drosophila PIM and THR are required for sister chromatid separation in mitosis and associate in vivo. Neither of these two proteins shares significant sequence similarity with known proteins. However, PIM has functional similarities with securin proteins. Like securin, PIM is degraded at the metaphase-to-anaphase transition and this degradation is required for sister chromatid separation. Securin binds and inhibits separase, a conserved cysteine endoprotease. Proteolysis of securin at the metaphase-to-anaphase transition activates separase, which degrades a conserved cohesin subunit, thereby allowing sister chromatid separation. To address whether PIM regulates separase activity or functions with THR in a distinct pathway, we have characterized a Drosophila separase homolog (SSE). SSE is an unusual member of the separase family. SSE is only about one-third the size of other separases and has a diverged endoprotease domain. However, our genetic analyses show that SSE is essential and required for sister chromatid separation during mitosis. Moreover, we show that SSE associates with both PIM and THR. Although our work shows that separase is required for sister chromatid separation in higher eukaryotes, in addition, it also indicates that the regulatory proteins have diverged to a surprising degree, particularly in Drosophila.

Amino Acid Sequence↗

PubMed2001

Development of retino-recipient projection neurons in the optic tectum of the chicken.

The dendritic development of a well-characterized retino-recipient neuronal type in the chicken optic tectum has been traced with intracellular labeling. Normal dendritic development can be divided into three phases: extension, differentiation and pruning. During the first phase, cells extend their dendrites, generate large dendritic fields and position their distal endings in a certain retino-recipient tectal layer. In the second phase, these dendritic endings arborize into characteristic bottlebrush-like structures, while the overall morphology of the neurons remains unaltered. After hatching, the number and width of the bottlebrush endings are reduced. The findings are discussed with respect to the innervation of the optic tectum by retinal afferents and possible guidance mechanisms for synapse formation in this system.

Animals↗

PubMed2000

Degradation of Drosophila PIM regulates sister chromatid separation during mitosis.

Drosophila Pimples (PIM) and Three rows (THR) are required for sister chromatid separation in mitosis. PIM accumulates during interphase and is degraded rapidly during mitosis. This degradation is dependent on a destruction box similar to that of B-type cyclins. Nondegradable PIM with a mutant destruction box can rescue sister chromatid separation in pim mutants but only when expressed at low levels. Higher levels of nondegradable PIM, as well as overexpression of wild-type PIM, inhibit sister chromatid separation. Moreover, cells arrested in mitosis before sister chromatid separation (by colcemid or by mutations in fizzy/CDC20) fail to degrade PIM. Thus, although not related by primary sequence, PIM has intriguing functional similarities to the securin proteins of budding yeast, fission yeast, and vertebrates. Whereas these securins are known to form a complex with separins, we show that PIM associates in vivo with THR, which does not contain the conserved separin domain.

Amino Acid Sequence↗

PubMed1999

Kinetoplastid RNA editing does not require the terminal 3' hydroxyl of guide RNA, but modifications to the guide RNA terminus can inhibit in vitro U insertion.

During RNA editing in kinetoplastid parasites, trans-acting guide RNAs (gRNAs) direct the insertion and deletion of U residues at precise sites in mitochondrial pre-mRNAs. We show here that some modifications to the 3' terminal ribose of gRNA inhibit its ability to direct in vitro U insertion. However, we found that gRNAs lacking this moiety in some circumstances support in vitro editing. Thus, the 3' OH is not required. Inhibition resulting from gRNA modification can be overcome by increasing the gRNA-pre-mRNA base-pairing potential upstream of the editing site, suggesting an importance for this interaction to productive processing.

Animals↗

PubMed1998

Association of guide RNA binding protein gBP21 with active RNA editing complexes in Trypanosoma brucei.

RNA editing in Trypanosoma brucei mitochondria produces mature mRNAs by a series of enzyme-catalyzed reactions that specifically insert or delete uridylates in association with a macromolecular complex. Using a mitochondrial fraction enriched for in vitro RNA editing activity, we produced several monoclonal antibodies that are specific for a 21-kDa guide RNA (gRNA) binding protein initially identified by UV cross-linking. Immunofluorescence studies localize the protein to the mitochondrion, with a preference for the kinetoplast. The antibodies cause a supershift of previously identified gRNA-specific ribonucleoprotein complexes and immunoprecipitate in vitro RNA editing activities that insert and delete uridylates. The immunoprecipitated material also contains gRNA-specific endoribonuclease, terminal uridylyltransferase, and RNA ligase activities as well as gRNA and both edited and unedited mRNA. The immunoprecipitate contains numerous proteins, of which the 21-kDa protein, a 90-kDa protein, and novel 55- and 16-kDa proteins can be UV cross-linked to gRNA. These studies indicate that the 21-kDa protein associates with the ribonucleoprotein complex (or complexes) that catalyze RNA editing.

Animals↗

PubMed1997

RNA editing: getting U into RNA.

RNA editing in kinetoplastid protozoa remodels the sequences of mitochondrial pre-mRNAs by the precise insertion and deletion of uridylate residues. These sequence changes are directed by small trans-acting RNAs, termed guide RNAs. The basic mechanistic pathway by which edited RNA is generated has recently been elucidated using in vitro systems capable of a full round of guide-RNA-directed editing.

Base Sequence↗

PubMed1997

RNA editing in kinetoplastid protozoa.

Mitochondrial transcripts in kinetoplastids undergo remarkable posttranscriptional editing by uridylate insertion and deletion. The often dramatic remodeling of pre-mRNA sequences is directed by small guide RNAs (gRNAs) to produce mature mRNAs. In vitro analyses of editing have been used to determine the mechanism of editing and show that editing occurs by a series of enzyme-catalyzed steps. They also show that chimeric gRNA/mRNA molecules are not editing intermediates as proposed but are aberrant end products of editing. The complexes and molecules that catalyze editing are now being identified and characterized. The origin of editing, its developmental regulation which helps control the switching between terminal respiratory systems during the life cycle of trypanosomes, and other areas for future study are discussed.

Animals↗

PubMed1996

RNA editing: a mechanism for gRNA-specified uridylate insertion into precursor mRNA.

In the mitochondria of trypanosomatid protozoa the precursors of messenger RNAs (pre-mRNAs) have their coding information remodeled by the site-specific insertion and deletion of uridylate (U) residues. Small trans-acting guide RNAs (gRNAs) supply the genetic information for this RNA editing. An in vitro system was developed to study the mechanism of U insertion into pre-mRNA. U-insertion editing occurs through a series of enzymatic steps that begin with gRNA-directed pre-mRNA cleavage. Inserted U's are derived from free uridine triphosphate and are added to the 3' terminus of a 5' pre-mRNA cleavage product. gRNA specifies edited RNA sequence at the subsequent ligation step by base pairing-mediated juxtaposition of the 3' cleavage product and the processed 5' cleavage product. gRNA/pre-mRNA chimeras, purported intermediates, seem to be abortive end products of the same reaction.

Animals↗

PubMed1996

Direct visualization of uridylate deletion in vitro suggests a mechanism for kinetoplastid RNA editing.

Deletion of uridylates from the 3'-most editing site of synthetic ATPase 6 pre-mRNA can be visualized directly by coincubation of a radiolabeled substrate RNA and a synthetic gRNA in 20S fractions of T.brucie mitochondrial lysates. Substrate RNA cleavage is gRNA directed and occurs 3' to the uridylates to be deleted. U residues appear to be sequentially removed from the 3' end of the 5' cleavage product prior to religation of the two pre-mRNA halves. gRNA/mRNA chimeric molecules are also produced. Time course experiments indicate that chimeras appear after cleavage intermediates and edited product. Furthermore, a mutant gRNA promotes formation of edited product but not detectable chimeras. Our results suggest a model for kinetoplastid RNA editing in which chimeric molecules are nonproductive end products of editing and not intermediates that serve as a repository for deleted U's.

Adenosine Triphosphatases↗

PubMed1996

A putative poststreptococcal case of OCD with chronic tic disorder, not otherwise specified.

A 12-year-old girl presented with an atypical, recurrent, increasingly treatment-resistant case of obsessive-compulsive disorder and chronic tic disorder associated with profound separation anxiety, learning difficulty, and intermittent upper respiratory symptoms. In addition to detailed reviews of history and findings from many clinical caretakers from the prior 7 years, current pediatric, psychiatric, neuropsychological, neuroimaging, and clinical laboratory data were also available. Treatment options were considered from multiple perspectives: psychoanalytically oriented psychotherapy, conventional pharmacotherapy, family interventions, cognitive-behavioral therapy, and learning-supportive strategies. Psychological, neuropsychiatric, and neuroimmunological formulations of etiology were considered. Subsequent treatments included supportive psychotherapy, neuroleptic augmentation of selective serotonin reuptake inhibitors, prophylactic penicillin, and a course of six sessions of plasmapheresis over a 2-week period. The case raises questions for ongoing consideration that juxtapose dynamic, neuropsychiatric, and neuroimmunological perspectives.

Antibiotic Prophylaxis↗

PubMed1994

Flexibility and interchangeability of polyadenylation signals in Saccharomyces cerevisiae.

Various signal motifs have been reported to be essential for proper mRNA 3'-end formation in the yeast Saccharomyces cerevisiae. However, none of these motifs has been shown to be sufficient to direct 3'-end processing and/or transcription termination. Therefore, several structural motifs have to act in concert for efficient 3'-end formation. In the region upstream of the three polyadenylation sites of the yeast gene for alcohol dehydrogenase I (ADH1), we have identified a hitherto unknown signal sequence contained within the octamer AAAAAAAA. This motif, located 11 nucleotides upstream of the first ADH1 polyadenylation site, is responsible for the utilization of this site in vitro and in vivo, since mutational alteration drastically reduced 3'-end formation at this position. Insertion of 38 ADH1-derived nucleotides encompassing the (A)8 motif into the 3'-end formation-deficient cyc1-512 deletion mutant restored full processing capacity in vitro. Insertion of the octamer alone did not restore 3'-end formation, although mutation of the (A)8 motif in the functional construct had abolished 3'-end processing activity almost completely. This demonstrates that the sequence AAAAAAAA is a necessary, although not sufficient, signal for efficient mRNA 3'-end formation in S. cerevisiae.

Alcohol Dehydrogenase↗

PubMed1992

Identification of pre-mRNA polyadenylation sites in Saccharomyces cerevisiae.

In contrast to higher eukaryotes, little is known about the nature of the sequences which direct 3'-end formation of pre-mRNAs in the yeast Saccharomyces cerevisiae. The hexanucleotide AAUAAA, which is highly conserved and crucial in mammals, does not seem to have any functional importance for 3'-end formation in yeast cells. Instead, other elements have been proposed to serve as signal sequences. We performed a detailed investigation of the yeast ACT1, ADH1, CYC1, and YPT1 cDNAs, which showed that the polyadenylation sites used in vivo can be scattered over a region spanning up to 200 nucleotides. It therefore seems very unlikely that a single signal sequence is responsible for the selection of all these polyadenylation sites. Our study also showed that in the large majority of mRNAs, polyadenylation starts directly before or after an adenosine residue and that 3'-end formation of ADH1 transcripts occurs preferentially at the sequence PyAAA. Site-directed mutagenesis of these sites in the ADH1 gene suggested that this PyAAA sequence is essential for polyadenylation site selection both in vitro and in vivo. Furthermore, the 3'-terminal regions of the yeast genes investigated here are characterized by their capacity to act as signals for 3'-end formation in vivo in either orientation.

Alcohol Dehydrogenase↗

PubMed1989

Cloning, characterization and heterologous expression of the SmaI restriction-modification system.

The genes coding for the class-II Serratia marcescens restriction-modification system have been cloned and expressed in E. coli. Recombinant clones, restricted incoming phage only poorly; the recombinant plasmids, however, became fully modified in vivo, i.e. completely resistant against digestion with R.SmaI. The determined nucleotide sequence of the cloned system revealed three open reading frames with lengths of 252 bp, 741 bp, and 876 bp. Through various deletion experiments and an insertion-mutation experiment the 876 bp open reading frame could be assigned to the SmaI DNA modification enzyme and the 741 bp open reading frame to the SmaI restriction endonuclease. Mapping of the transcription start sites of the genes revealed that the SmaI endonuclease is transcribed as polycistronic mRNA together with a 252 bp long preceding open reading frame of unknown function. No homology was found when comparing the amino acid sequence of M.SmaI with the published sequences of m5C-specific DNA modification methyltransferases. On the other hand, a stretch of 14 amino acids in the C-proximal region of M.SmaI shows a significant homology to the C-proximal amino acid sequences of the N6A-methyltransferases M.HinfI and M.DpnIIA and the N4C-methyltransferase M.PvuII.

Amino Acid Sequence↗