Biomedical subjects

M Mischke

Publications and source records attributed to M Mischke.

3 recordsLinked to original sources

PubMed2000

Cell cycle programs of gene expression control morphogenetic protein localization.

Genomic studies in yeast have revealed that one eighth of genes are cell cycle regulated in their expression. Almost without exception, the significance of cell cycle periodic gene expression has not been tested. Given that many such genes are critical to cellular morphogenesis, we wanted to examine the importance of periodic gene expression to this process. The expression profiles of two genes required for the axial pattern of cell division, BUD3 and BUD10/AXL2/SRO4, are strongly cell cycle regulated. BUD3 is expressed close to the onset of mitosis. BUD10 is expressed in late G1. Through promotor-swap experiments, the expression profile of each gene was altered and the consequences examined. We found that an S/G2 pulse of BUD3 expression controls the timing of Bud3p localization, but that this timing is not critical to Bud3p function. In contrast, a G1 pulse of BUD10 expression plays a direct role in Bud10p localization and function. Bud10p, a membrane protein, relies on the polarized secretory machinery specific to G1 to be delivered to its proper location. Such a secretion-based targeting mechanism for membrane proteins provides cells with flexibility in remodeling their architecture or evolving new forms.

Cell Cycle↗

PubMed1995

Role of Bud3p in producing the axial budding pattern of yeast.

Yeast cells can select bud sites in either of two distinct spatial patterns. a cells and alpha cells typically bud in an axial pattern, in which both mother and daughter cells form new buds adjacent to the preceding division site. In contrast, a/alpha cells typically bud in a bipolar pattern, in which new buds can form at either pole of the cell. The BUD3 gene is specifically required for the axial pattern of budding: mutations of BUD3 (including a deletion) affect the axial pattern but not the bipolar pattern. The sequence of BUD3 predicts a product (Bud3p) of 1635 amino acids with no strong or instructive similarities to previously known proteins. However, immunofluorescence localization of Bud3p has revealed that it assembles in an apparent double ring encircling the mother-bud neck shortly after the mitotic spindle forms. The Bud3p structure at the neck persists until cytokinesis, when it splits to yield a single ring of Bud3p marking the division site on each of the two progeny cells. These single rings remain for much of the ensuing unbudded phase and then disassemble. The Bud3p rings are indistinguishable from those of the neck filament-associated proteins (Cdc3p, Cdc10p, Cdc11p, and Cdc12p), except that the latter proteins assemble before bud emergence and remain in place for the duration of the cell cycle. Upon shift of a temperature-sensitive cdc12 mutant to restrictive temperature, localization of both Bud3p and the neck filament-associated proteins is rapidly lost. In addition, a haploid cdc11 mutant loses its axial-budding pattern upon shift to restrictive temperature. Taken together, the data suggest that Bud3p and the neck filaments are linked in a cycle in which each controls the position of the other's assembly: Bud3p assembles onto the neck filaments in one cell cycle to mark the site for axial budding (including assembly of the new ring of neck filaments) in the next cell cycle. As the expression and localization of Bud3p are similar in a, alpha, and a/alpha cells, additional regulation must exist such that Bud3p restricts the position of bud formation in a and alpha cells but not in a/alpha cells.

Amino Acid Sequence↗

PubMed1994

A single p34cdc2 protein kinase (encoded by nimXcdc2) is required at G1 and G2 in Aspergillus nidulans.

We have cloned and sequenced a homolog of cdc2 from Aspergillus nidulans that can complement the Schizosaccharomyces pombe cdc2-33 mutation. The gene was deleted and is required for continued nuclear DNA replication but not for mitochondrial DNA replication. Three different temperature-sensitive alleles were generated by reverse genetics. All of the mutations generate the nim phenotype of A. nidulans. The new gene was designated nimXcdc2 as it is not allelic to any of the other nim genes (nimA to nimW) of A. nidulans. Reciprocal shift experiments place an essential function for nimXcdc2 in G1 and G2. Antipeptide antibodies were generated that detect NIMXcdc2, and antisera were also generated to detect NIMEcyclinB. The two p34cdc2 protein species previously detected in A. nidulans, p34 and p37, both precipitate using NIMXcdc2 C-terminus-specific antibodies but only p34 co-precipitates with NIMEcyclinB. Dephosphorylation of denatured p34 converts it to the p37 form, showing p37 to be the non-phosphorylated form of NIMXcdc2. The phosphorylation of p34 is therefore associated with its interaction with NIMEcyclinB.

Amino Acid Sequence↗