Structure and functional analysis of a molecular switch that regulated the mRNA synthesis rate.

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The transcription elongation factor DSIF, which is comprised of human Spt4 and Spt5, is unique in its ability to regulate RNA polymerase II processivity. Experiments with cultured HeLa cells and in vitro transcription assays revealed that stimulation of transcription by the DNA-binding transcription activator Ga14VP16 is dependent on human Spt5, indicating that actively transcribed genes require DSIF activity. Microarray analysis revealed that approximately 7.5% of genes decreased their expression by a specific morpholino antisense-mediated knockdown of zebrafish Spt5. Further investigation of the down-regulated genes showed that the genes most intensely repressed by the knockdown were strongly activated during early development in untreated embryos, supporting above results. On the other hand, cooperative action of DSIF and the transcription elongation factor NELF negatively regulates transcription elongation by RNA polymerase II. In this study, I show that DSIF and NELF contribute to the regulation of junB gene expression not only by pausing RNA polymerase II elongation at promoter proximal region before cytokine IL-6 induction, but also by attenuating mRNA induction level after induction. In addition, two deletion mutants of human Spt5 have been isolated to elucidate the regulatory mechanisms of the mRNA synthesis rate.