We describe a straightforward PCR-based approach to the deletion, tagging, and overexpression of genes in their normal chromosomal locations in the fission yeast Schizosaccharomyces pombe. Using this approach and the S. pombe ura4+ gene as a marker, nine genes were deleted with efficiencies of homologous integration ranging from 6 to 63%. We also constructed a series of plasmids containing the kanMX6 module, which allows selection of G418-resistant cells and thus provides a new heterologous marker for use in S. pombe. The modular nature of these constructs allows a small number of PCR primers to be used for a wide variety of gene manipulations, including deletion, overexpression (using the regulatable nmt1 promoter), C- or N-terminal protein tagging (with HA, Myc, GST, or GFP), and partial C- or N-terminal deletions with or without tagging. Nine genes were manipulated using these kanMX6 constructs as templates for PCR. The PCR primers included 60 to 80 bp of flanking sequences homologous to target sequences in the genome. Transformants were screened for homologous integration by PCR. In most cases, the efficiency of homologous integration was > or = 50%, and the lowest efficiency encountered was 17%. The methodology and constructs described here should greatly facilitate analysis of gene function in S. pombe.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/%28SICI%291097-0061%28199807%2914%3A10%3C943%3A%3AAID-YEA292%3E3.0.CO%3B2-Y

Heterologous modules for efficient and versatile PCR-based gene targeting in Schizosaccharomyces pombe

PEST sequences and regulation by proteolysis

SKP1 connects cell cycle regulators to the ubiquitin proteolysis machinery through a novel motif, the F-box.

Oscillations in the activity of cyclin-dependent kinases (CDKs) promote progression through the eukaryotic cell cycle. This review examines how proteolysis regulates CDK activity—by degrading CDK activators or inhibitors—and also how proteolysis may directly trigger the transition from metaphase to anaphase. Proteolysis during the cell cycle is mediated by two distinct ubiquitin-conjugation pathways. One pathway, requiring CDC34, initiates DNA replication by degrading a CDK inhibitor. The second pathway, involving a large protein complex called the anaphase-promoting complex or cyclosome, initiates chromosome segregation and exit from mitosis by degrading anaphase inhibitors and mitotic cyclins. Proteolysis therefore drives cell cycle progression not only by regulating CDK activity, but by directly influencing chromosome and spindle dynamics.

https://science.sciencemag.org/content/sci/274/5293/1652.full.pdf

How proteolysis drives the cell cycle

We have previously identified a candidate oncogene (PRAD1 or D11S287E) on chromosome 11q13 which is clonally rearranged with the parathyroid hormone locus in a subset of benign parathyroid tumours. We now report that a cloned human placental PRAD1 complementary DNA encodes a protein of 295 amino acids with sequence similarities to the cyclins. Cyclins can form a complex with and activate p34cdc2 protein kinase, thereby regulating progress through the cell cycle. PRAD 1 messenger RNA levels vary dramatically across the cell cycle in HeLa cells. Addition of the PRAD1 protein to interphase clam embryo lysates containing inactive p34cdc2 kinase and lacking endogenous cyclins allows it to be isolated using beads bearing p13suc1, a yeast protein that binds cdc2 and related kinases with high affinity and coprecipitates kinase-associated proteins. Addition of PRAD1 also induces phosphorylation of histone H1, a preferred substrate of cdc2. These data suggest that PRAD1 encodes a novel cyclin whose overexpression may play an important part in the development of various tumours with abnormalities in 11q13.

A novel cyclin encoded by a bcl1 -linked candidate oncogene

WHI1-1 is a dominant mutation that reduces cell volume by allowing cells to commit to division at abnormally small sizes, shortening the G1 phase of the cell cycle. The gene was cloned, and dosage studies indicated that the normal gene activated commitment to division in a dose-dependent manner, and that the mutant gene had a hyperactive but qualitatively similar function. Mild over-expression of the mutant gene eliminated G1 phase, apparently entirely relaxing the normal G1 size control, but revealing hitherto cryptic controls. Sequence analysis showed that the hyperactivity of the mutant was caused by the loss of the C-terminal third of the wild-type protein. This portion of the protein contained PEST regions, which may be signals for protein degradation. The WHI1 protein had sequence similarity to clam cyclin A, to sea urchin cyclin and to Schizosaccharomyces pombe cdc13, a cyclin homolog. Since cyclins are inducers of mitosis, WHI1 may be a direct regulator of commitment to division. A probable accessory function of the WHI1 activator is to assist recovery from alpha factor arrest; WHI1-1 mutant cells could not be permanently arrested by pheromone, consistent with a hyperactivation of division.

The WHI1+ gene of Saccharomyces cerevisiae tethers cell division to cell size and is a cyclin homolog.

In Saccharomyces cerevisiae, several of the proteins involved in the Start decision have been identified; these include the Cdc28 protein kinase and three cyclin-like proteins, Cln1, Cln2 and Cln3. We find that Cln3 is a very unstable, low abundance protein. In contrast, the truncated Cln3-1 protein is stable, suggesting that the PEST-rich C-terminal third of Cln3 is necessary for rapid turnover. Cln3 associates with Cdc28 to form an active kinase complex that phosphorylates Cln3 itself and a co-precipitated substrate of 45 kDa. The cdc34-2 allele, which encodes a defective ubiquitin conjugating enzyme, dramatically increases the kinase activity associated with Cln3, but does not affect the half-life of Cln3. The Cln--Cdc28 complex is inactivated by treatment with non-specific phosphatases; prolonged incubation with ATP restores kinase activity to the dephosphorylated kinase complex. It is thus possible that phosphate residues essential for Cln-Cdc28 kinase activity are added autocatalytically. The multiple post-translational controls on Cln3 activity may help Cln3 tether division to growth.

The Cln3-Cdc28 kinase complex of S. cerevisiae is regulated by proteolysis and phosphorylation.

It has been known for a decade that in yeast, the CDC28 gene of Saccharomyces cerevisiae and the cdc2+ gene of Schizosaccharomyces pombe are needed at two points in their host's cell cycles: once in G1 phase, for commitment to division, and once again in mitosis (Nurse and Bissett 1981; Piggott et al. 1982). These two genes encode highly homologous proteins, which have proven to be the catalytic subunits of protein kinases (Reed et al. 1985; Simanis and Nurse 1986). The active protein kinase is a complex containing the Cdc28/cdc2 protein and a protein called a cyclin (Draetta et al. 1989). Other subunits may also be present (Brizuela et al. 1987.

R. Nash

Papers

The WHI1+ gene of Saccharomyces cerevisiae tethers cell division to cell size and is a cyclin homolog.

The Cln3-Cdc28 kinase complex of S. cerevisiae is regulated by proteolysis and phosphorylation.

Characterization of G1 and mitotic cyclins of budding yeast