The availability of cloned cDNAs encoding the four subunits of the Torpedo acetylcholine receptor, which can be expressed to make functional receptors in Xenopus oocytes, has made possible a detailed investigation of the functions of the different structural components of the receptor. The functional analysis of receptors with α-subunits altered at specific sites by site-directed mutagenesis of the cDNA has allowed the location of specific regions of the α-subunit molecule involved in acetylcholine binding and forming a transmembrane ionic channel.

Location of functional regions of acetylcholine receptor α-subunit by site-directed mutagenesis

The cloned cDNAs encoding the four subunits of the Torpedo californica acetylcholine receptor, each carried by a simian virus 40 vector, direct the synthesis of the functional receptor in a combined expression system consisting of COS monkey cells and Xenopus oocytes. Our results suggest that all four subunits are required to elicit a normal nicotinic response to acetylcholine, whereas only the alpha-subunit is indispensable for alpha-bungarotoxin binding activity.

Expression of functional acetylcholine receptor from cloned cDNAs

I. Introduction THE POMC gene encodes the complex precursor to a variety of biologically active, important neuromodulator and endocrine peptides. It is expressed in a variety of tissues in the mammal, but its main site of expression is the pituitary anterior lobe cortocotroph and intermediate lobe melanotroph. The POMC molecule is posttranslationally processed to different biologically active peptides in these two cell types, with ACTH, β-lipotropin, and β-endorphin being major products in the corticotroph and α-MSH, corticotropin-like intermediate lobe peptide, and acetyl-β-endorphin in the melanotroph (1). This array of different biological activities derived from the POMC molecule possibly necessitates the observed complex regulation of POMC peptide secretion and POMC gene expression in pituitary. Regulation of POMC peptide secretion has recently been reviewed in several places (2, 3). This review will deal primarily with the regulation of POMC gene expression in rat and mouse pituitary tissues, the sp...

Regulation of Proopiomelanocortin Gene Expression in Pituitary

The present study was designed to examine the role of the nurr1/nur77 subfamily of nuclear receptor transcription factors in the regulation of the hypothalamic/pituitary/adrenal axis at the neuroendocrine level. We demonstrate that this nuclear receptor subfamily can regulate the expression of the CRF and POMC genes by interacting with a specific cis-acting sequence in their proximal promoter regions. To examine the physiological significance of this response, we have focused on the POMC gene. We provide evidence that nurr1 and nur77 are rapidly induced by CRF in primary pituitary cells and that this induction is mimicked by forskolin in an anterior pituitary cell line. Further, we demonstrate that both nurr1- and forskolin-dependent induction of a POMC-chloramphenicol acetyltransferase reporter gene are inhibited by mutation of the nurr1-binding site within the POMC promoter and that this site alone can confer cAMP responsiveness to a heterologous promoter. Finally, we provide evidence that the nurr1/nur77 response sequence is pivotal to both nurr1/nur77-dependent positive regulation and glucocorticoid receptor-dependent negative regulation of the POMC gene. These data strongly support the conclusion that the nurr1/nur77 subfamily plays an important coordinate neuroendocrine-regulatory role at all levels of the hypothalamic/pituitary/adrenal axis.

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Neuroendocrine regulation of the hypothalamic pituitary adrenal axis by the nurr1/nur77 subfamily of nuclear receptors.

Light induction of chloroplast maturation in plant seedlings (‘greening’) is associated with the induction in expression of the enzyme ribulose 1,5-bisphosphate carboxylase. To define the regions of a gene encoding the small subunit of ribulose 1,5-bisphosphate carboxylase involved in light inducibility of pea plants, we have introduced derivatives of the gene into petunia cells using a tumour-inducing plasmid vector. A conserved 33-base pair sequence close to the ‘TATA’ box of the gene is sufficient to confer light inducibility of the small subunit gene.

A short conserved sequence is involved in the light-inducibility of a gene encoding ribulose 1,5-bisphosphate carboxylase small subunit of pea

The cloned human corticotropin-beta-lipotropin precursor gene, when joined with an SV40 vector and introduced into COS monkey cells, is transcribed from its own promoter. The DNA sequences required for promoter function have been identified by using 5' deletion mutants of the fusion gene AT which contains the 5'-flanking sequence and capping site of the human corticotropin-beta-lipotropin precursor gene and the structural sequence of the herpes simplex virus thymidine kinase gene. The deletion of the sequence located between 53 and 59 bp upstream of the capping site enhances the transcription approximately 3-fold, while the deletion of the TATA box region abolishes the transcription.

https://www.embopress.org/doi/pdf/10.1002/j.1460-2075.1982.tb01351.x

T Kurosaki

Papers

DNA sequences required for transcription in vivo of the human corticotropin-beta-lipotropin precursor gene.