PHARMACOLOGY

 TYPE IV:: 

GENE TRANSCRIPTION REGULATORY RECEPTORS OR NUCLEAR RECEPTORS ::

    Like kinase -linked receptors these receptors also control gene transcription however these receptors are located intracellularly on nuclear membrane or within cytosol These receptors take hours to produce their effects Receptors for steroid hormones thyroid hormone and other agents such as retinoic acid and vitamin D belong to this superfamily of receptors 

            Basic structure of these receptors consists of large monomeric proteins of 400-1000 residues containing a highly conserved region of 60 residues in the middle of the molecule which constitutes the DNA binding domain of the receptor This DNA binding domain contains two loop of about 15 residues each (zinc fingers) knotted together by a cluster of four cysteine residues surrounding a zinc atom The hormone -binding domain lies in the down stream of the central region of DNA helix while in the upstream lies a variable region which is responsible for controlling gene-transcription These receptors promote or repress the particular genes pattern of gene activation depends on both cell type and nature of ligand and so they are highly diversified Effect of the receptor stimulation are produced as a result of altered protein synthesis 

Ion Channels and Enyzmes as Drug Targets ::

    From the above discussion it is clear that ion channels (linked to Type 1 receptors) may serve as the target for the action of drugs Ion channels are formed by the proteins some of the classical examples of ion channels serving as targets for drugs