Abstract
In Schizosaccharomyces pombe the nuclear-localized Lsk1p-Lsc1p cyclin dependent kinase complex promotes Ser-2 phosphorylation of the heptad repeats found within the RNA pol II carboxy terminal domain (CTD). Here, we first provide evidence supporting the existence of a third previously uncharacterized Ser-2 CTD kinase subunit, Lsg1p. As expected for a component of the complex, Lsg1p localizes to the nucleus, promotes Ser-2 phosphorylation of the CTD, and physically interacts with both Lsk1p and Lsc1p in vivo. Interestingly, we also demonstrate that lsg1Δ mutants – just like lsk1Δ and lsc1Δ strains – are compromised in their ability to faithfully and reliably complete cytokinesis. Next, to address whether kinase mediated alterations in CTD phosphorylation might selectively alter the expression of genes with roles in cytokinesis and/or the cytoskeleton, global gene expression profiles were analyzed. Mutants impaired in Ser-2 phosphorylation display little change with respect to the level of transcription of most genes. However, genes affecting cytokinesis – including the actin interacting protein gene, aip1 – as well as genes with roles in meiosis, are included in a small subset that are differentially regulated. Significantly, genetic analysis of lsk1Δ aip1Δ double mutants is consistent with Lsk1p and Aip1p acting in a linear pathway with respect to the regulation of cytokinesis.
Highlights
In Schizosaccharomyces pombe, just as in developmentally complex metazoans, cytokinesis is mediated through the assembly and constriction of a contractile, actomyosin ring [1]
Ser-2 carboxy terminal domain (CTD) kinase complexes in fungi consist of i) a catalytic kinase subunit, ii) a regulatory cyclin subunit, and iii) a regulatory ‘‘gamma’’ subunit [24]
We identify the gene product of the S. pombe ORF, SPCC4B3.08, as a bona fide member of the fission yeast Ser-2 CTD kinase complex
Summary
In Schizosaccharomyces pombe, just as in developmentally complex metazoans, cytokinesis is mediated through the assembly and constriction of a contractile, actomyosin ring [1]. Given the importance of cytokinesis in cellular growth and development, it is not surprising that evidence supporting the existence of a cytokinesis monitoring system has emerged in S. pombe This system has the capacity to both delay G2/M progression and stabilize the actomyosin ring upon perturbation of the division machinery and aids in the faithful and reliable execution of fission yeast cytokinesis [9,10]. While the loss of clp results in only weak cytokinesis defects under normal growth conditions, clp1D cells display a lethal multi-nucleate phenotype when treated with drugs (Latrunculin A) that perturb the normal function of the actomyosin ring These defects are in part due to the inability of clp1D cells to prolong the duration of SIN signaling [9,10]. – as demonstrated by genetic analysis with hypo- and hyper-active SIN mutants – Lsk1p promotes SIN activation [11]
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