Transcriptional repression by neuron-restrictive silencer factor is mediated via the Sin3-histone deacetylase complex.

A large number of neuron-specific genes characterized to date are under the control of negative transcriptional regulation. Many promoter regions of neuron-specific genes possess the repressor element repressor element 1/neuron-restrictive silencing element (RE1/NRSE). Its cognate binding protein, REST/NRSF, is an essential transcription factor; its null mutations result in embryonic lethality, and its dominant negative mutants produce aberrant expression of neuron-specific genes. REST/NRSF acts as a regulator of neuron-specific gene expression in both nonneuronal tissue and developing neurons. Here, we shown that heterologous expression of REST/NRSF in Saccharomyces cerevisiae is able to repress transcription from yeast promoters engineered to contain RE1/NRSEs. Moreover, we have taken advantage of this observation to show that this repression requires both yeast Sin3p and Rpd3p and that REST/NRSF physically interacts with the product of the yeast SIN3 gene in vivo. Furthermore, we show that REST/NRSF binds mammalian SIN3A and HDAC-2 and requires histone deacetylase activity to repress neuronal gene transcription in both nonneuronal and neuronal cell lines. We show that REST/NRSF binding to RE1/NRSE is accompanied by a decrease in the acetylation of histones around RE1/NRSE and that this decrease requires the N-terminal Sin3p binding domain of REST/NRSF. Taken together, these data suggest that REST/NRSF represses neuronal gene transcription by recruiting the SIN3/HDAC complex.

Repression and activation of muscarinic receptor genes.

The specific cellular response to muscarinic receptor activation is dependent upon appropriate expression of each of the five muscarinic receptor genes by individual cells. Here we summarise recent work describing some of the genomic regulatory elements and transcriptional mechanisms that control expression of the M1 and M4 genes.

Functional analysis of a chimeric mammalian peptide transporter derived from the intestinal and renal isoforms.

l. Recently two genes have been identified by expression cloning that encode mammalian epithelial peptide transporters capable of translocating di- and tripeptides and selected peptidomimetics by stereoselective and rheogenic substrate-H+ cotransport. PepT1 from rabbit or human small intestine induces a transport activity with high transport capacity but rather low substrate affinity when expressed in Xenopus oocytes. In contrast, the renal carrier PepT2 is a high affinity-type transporter with a lower maximal transport capacity. In addition, both transporters show differences in pH dependence and substrate specificity. 2. As a first approach to identify structural components of the transport proteins that determine their phenotypical characteristics, we constructed a recombinant chimeric peptide transporter (CH1Pep) in which the aminoterminal region (residues 1-401) is derived from PepT2 whereas the carboxyterminal region (residues 402-707) starting at the end of transmembrane domain 9 is derived from PepT1. Expression of PepT1, PepT2 and CH1Pep in Xenopus oocytes allowed the characteristics of the transporters to be determined by flux studies employing a radiolabelled dipeptide and by the two-electrode voltage clamp technique. 3. Our studies indicate that CH1Pep conserves the characteristics of PepT2 including the high affinity for dipeptides and peptidomimetics, the substrate specificity, the pH dependence of transport activation and the electrophysiological parameters. We conclude that the phenotypical characteristics of the renal peptide transporter are determined by its amino-terminal region.