| 1. |
- Fülöp, Katalin, et al.
(författare)
-
Arabidopsis anaphase-promoting complexes : multiple activators and wide range of substrates might keep APC perpetually busy
- 2005
-
Ingår i: Cell Cycle. - Austin : Landes bioscience. - 1538-4101 .- 1551-4005. ; 4:8, s. 1084-1092
-
Tidskriftsartikel (refereegranskat)abstract
- The anaphase-promoting complex (APC), a multisubunit E3 ubiquitin ligase, is an essential regulator of the cell cycle from metaphase until S phase in yeast and metazoans. APC mediates degradation of numerous cell cycle-related proteins, including mitotic cyclins and its activation and substrate-specificity are determined by two adaptor proteins, Cdc20 and Cdh1. Plants have multiple APC activators and the Cdh1-type proteins, in addition, are represented by two subclasses, known as Ccs52A and Ccs52B. The Arabidopsis genome contains five cdc20 genes as well as ccs52A1, ccs52A2 and ccs52B.In Schizosaccharomyces pombe, expression of the three Atccs52 genes elicited distinct phenotypes supporting nonredundant function of the AtCcs52 proteins. Consistent with these activities, the AtCcs52 proteins were able to bind both to the yeast and the Arabidopsis APCs. In synchronized Arabidopsis cell cultures the cdc20 transcripts were present from early G2 until the M-phase exit, ccs52B from G2/M to M while ccs52A1 and ccs52A2 were from late M until early G2, suggesting consecutive action of these APC activators in the plant cell cycle. The AtCcs52 proteins interacted with different subsets of mitotic cyclins, in accordance with their expression profiles, either in free- or CDK-bound forms. Expression of most APC subunits was constitutive, whereas cdc27a and cdc27b, corresponding to two forms of apc3, and ubc19 and ubc20 encoding E2-C type ubiquitin-conjugating enzymes displayed differences in their cell cycle regulation. These data indicate the existence of numerous APC(Cdc20/Ccs52/Cdc27) forms in Arabidopsis, which in conjunction with different E2 enzymes might have distinct or complementary functions at distinct stages of the cell cycle.
|
|
| 2. |
- Kevei, Eva, et al.
(författare)
-
Forward genetic analysis of the circadian clock separates the multiple functions of ZEITLUPE.
- 2006
-
Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 140:3, s. 933-45
-
Tidskriftsartikel (refereegranskat)abstract
- The circadian system of Arabidopsis (Arabidopsis thaliana) includes feedback loops of gene regulation that generate 24-h oscillations. Components of these loops remain to be identified; none of the known components is completely understood, including ZEITLUPE (ZTL), a gene implicated in regulated protein degradation. ztl mutations affect both circadian and developmental responses to red light, possibly through ZTL interaction with PHYTOCHROME B (PHYB). We conducted a large-scale genetic screen that identified additional clock-affecting loci. Other mutants recovered include 11 new ztl alleles encompassing mutations in each of the ZTL protein domains. Each mutation lengthened the circadian period, even in dark-grown seedlings entrained to temperature cycles. A mutation of the LIGHT, OXYGEN, VOLTAGE (LOV)/Period-ARNT-Sim (PAS) domain was unique in retaining wild-type responses to red light both for the circadian period and for control of hypocotyl elongation. This uncoupling of ztl phenotypes indicates that interactions of ZTL protein with multiple factors must be disrupted to generate the full ztl mutant phenotype. Protein interaction assays showed that the ztl mutant phenotypes were not fully explained by impaired interactions with previously described partner proteins Arabidopsis S-phase kinase-related protein 1, TIMING OF CAB EXPRESSION 1, and PHYB. Interaction with PHYB was unaffected by mutation of any ZTL domain. Mutation of the kelch repeat domain affected protein binding at both the LOV/PAS and the F-box domains, indicating that interaction among ZTL domains leads to the strong phenotypes of kelch mutations. Forward genetics continues to provide insight regarding both known and newly discovered components of the circadian system, although current approaches have saturated mutations at some loci.
|
|
