BLG-e1 - a novel regulatory element in the distal region of the beta-lactoglobulin gene promoter

beta-Lactoglobulin (BLG) is a major ruminant milk protein. A regulatory element, termed BLG-e1, was defined in the distal region of the ovine BLG gene promoter. This 299-bp element lacks the established cis-regulatory sequences that affect milk-protein gene expression. Nevertheless, it alters the binding of downstream BLG sequences to histone H4 and the sensitivity of the histone-DNA complexes to trichostatin A treatment. In mammary cells cultured under favorable lactogenic conditions, BLG-e1 acts as a potent, position-independent silencer of BLG/luciferase expression, and similarly affects the promoter activity of the mouse whey acidic protein gene. Intragenic sequences upstream of BLG exon 2 reverse the silencing effect of BLG-e1 in vitro and in transgenic mice.     

Structural basis of a transcription pre-initiation complex on a divergent promoter

1. Download : Download high-res image (273KB)
2. Download : Download full-size image

     

Differential contribution to gene expression prediction of histone modifications at enhancers or promoters

The ChIP-seq signal of histone modifications at promoters is a good predictor of gene expression in different cellular contexts, but whether this is also true at enhancers is not clear. To address this issue, we develop quantitative models to characterize the relationship of gene expression with histone modifications at enhancers or promoters. We use embryonic stem cells (ESCs), which contain a full spectrum of active and repressed (poised) enhancers, to train predictive models. As many poised enhancers in ESCs switch towards an active state during differentiation, predictive models can also be trained on poised enhancers throughout differentiation and in development. Remarkably, we determine that histone modifications at enhancers, as well as promoters, are predictive of gene expression in ESCs and throughout differentiation and development. Importantly, we demonstrate that their contribution to the predictive models varies depending on their location in enhancers or promoters. Moreover, we use a local regression (LOESS) to normalize sequencing data from different sources, which allows us to apply predictive models trained in a specific cellular context to a different one. We conclude that the relationship between gene expression and histone modifications at enhancers is universal and different from promoters. Our study provides new insight into how histone modifications relate to gene expression based on their location in enhancers or promoters.     

Immunoglobulin carbohydrate requirement for formation of an IgG-IgG complex.

In addition to their Fc oligosaccharides, some immunoglobulin molecules have oligosaccharides linked to variable segments of H or L chains. These Fab oligosaccharides are potential determinants of antibody specificity. This possibility was considered in a study of the IgG antiglobulin from a patient with IgG-IgG complexes. F(ab')2 fragments of the antiglobulin retained the ability to form complexes with normal IgG as detected by analytical ultracentrifugation. Removal of F(ab')2 sialic acids by neuraminidase abolished complex formation. Recombination experiments further localized antiglobulin activity to the L chains. Antiglobulin activity of the recombinant molecules was shown by analytical ultracentrifugation and by column chromatography with molecules containing 125I-labeled L chains. L chains from the subject's IgG were enriched in sialic acids. Thus, a sialic acid-containing oligosaccharide on the L chain of this antiglobulin is required for its binding action.     

Dephosphorylation of the pre-initiation complex is critical for origin firing

1. Download : Download high-res image (110KB)
2. Download : Download full-size image