RESUMO
In the yeast Saccharomyces cerevisiae, the MADS-box protein Mcm1, which is highly related to mammalian SRF (serum response factor), forms a ternary complex with SFF (Swi five factor) to regulate the cell cycle expression of genes such as SWI5, CLB2 and ACE2. Here we show that the forkhead protein Fkh2 is a component of SFF and is essential for ternary complex formation on the SWI5 and ACE2 promoters. Fkh2 is essential for the correct cell cycle periodicity of SWI5 and CLB2 gene expression and is phosphorylated with a timing that is consistent with a role in this expression. Furthermore, investigation of the relationship between Fkh2 and a related forkhead protein Fkh1 demonstrates that these proteins act in overlapping pathways to regulate cell morphology and cell separation. This is the first example of a eukaryotic transcription factor complex containing both a MADS-box and a forkhead protein, and it has important implications for the regulation of mammalian gene expression.
Assuntos
Proteínas de Ciclo Celular , Ciclo Celular/genética , Regulação Fúngica da Expressão Gênica , Proteínas Nucleares/metabolismo , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/genética , Fatores de Transcrição/química , Fatores de Transcrição/metabolismo , Núcleo Celular/metabolismo , Sequência Consenso/genética , Ciclina B/genética , Ciclina B/metabolismo , Ciclinas/genética , DNA Fúngico/genética , DNA Fúngico/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Fatores de Transcrição Forkhead , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Fase G2/genética , Deleção de Genes , Genes Fúngicos/genética , Proteína 1 de Manutenção de Minicromossomo , Proteínas Nucleares/genética , Fosforilação , Regiões Promotoras Genéticas/genética , Ligação Proteica , RNA Mensageiro/metabolismo , Elementos de Resposta/genética , Saccharomyces cerevisiae/citologia , Saccharomyces cerevisiae/metabolismo , Fuso Acromático/metabolismo , Fatores de Transcrição/genéticaRESUMO
Previous data have indicated the presence of c-myc mRNA and protein in mature skeletal muscle, but whether the protein is present as a Myc/Max heterodimer capable of influencing transcription in that tissue or its potential role in pathological muscle tissue has not been examined. The expression of c-myc in normal and mdx dystrophic mouse skeletal muscle was therefore investigated. C-myc mRNA was detected by Northern hybridisation in normal and dystrophic mouse muscle from mice up to 40 days of age and immunohistochemical staining confirmed that c-myc protein was expressed in muscle fibre nuclei in the muscles of mice up to 40 days of age. The presence of Myc-containing complexes that are able to bind to the concensus Myc/Max binding site was demonstrated in these muscles using the electrophoretic mobility shift assay. These results show that c-myc protein is expressed in functional complexes in both normal and dystrophic mouse skeletal muscle during post-natal maturation. They also show that expression of c-myc in mouse skeletal muscle decreases to undetectable levels by about 40 days of age. Although no differences were detected between the expression of c-myc in mdx and control mouse muscle, these data show that muscle contains Myc protein which has previously been demonstrated to be capable of initiating programmed cell death in other tissues.
