Claire Fraser

The Minimal Gene Complement of Mycoplasma genitalium

The complete nucleotide sequence (580,070 base pairs) of the Mycoplasma genitalium genome, the smallest known genome of any free-living organism, has been determined by whole-genome random sequencing and assembly. A total of only 470 predicted coding regions were identified that include genes required for DNA replication, transcription and translation, DNA repair, cellular transport, and energy metabolism. Comparison of this genome to that of Haemophilus influenzae suggests that differences in genome content are reflected as profound differences in physiology and metabolic capacity between these two organisms.

β-Adrenergic receptors

Publisher Summary β-adrenergic receptors mediate the physiological responses of the catecholamines, epinephrine and norepinephrine and modulate a myriad of physiological functions including relaxation of smooth muscle, chronotropic and inotropic cardiac responses, and lipolysis in adipose tissue. Pharmacologic and functional studies have revealed that β-adrenergic receptors are found in nearly all mammalian tissues and represent a heterogeneous population. β-adrenergic receptors were originally classified into two subtypes, β 1 - and β 2 -adrenergic receptors, based on the relative potency of epinephrine and norepinephrine. The β 1 -adrenergic receptor is equally responsive to these two agonists; the β 2 -adrenergic receptor is more potently stimulated by epinephrine. More recently, molecular cloning techniques have led to the discovery of an additional receptor subtype, the β 3 -adrenergic receptor. This subtype is preferentially expressed in adipose tissue and displays a higher sensitivity to norepinephrine and a series of novel β-adrenergic agonists having thermogenic, anti-obesity, and anti-diabetic activities and a lower affinity for classical β-adrenergic blockers as compared to β 1 - and β 2 -adrenergic receptors. Molecular biology has proven invaluable as a tool for the elucidation of the gene structure of β-adrenergic receptors and thus, has provided the opportunity to analyze receptor subtypes, receptor structure, ligand binding, and G protein coupling at the molecular level, as well as providing a model system for the study of other G protein-coupled receptors. Some of the new information on β-receptor structure and function derived from the application of molecular biology to receptor studies is summarized in this chapter.

Monoclonal Antibodies to Integral Membrane Transport and Receptor Proteins

The isolation and molecular characterization of integral membrane proteins of major physiological significance, including receptors and transport proteins, are at best difficult tasks. For good results a multifaceted approach to elucidating the structure and function of membrane proteins is required. Useful approaches include affinity labeling and photoaffinity labeling (Ruoho et al, 1984), radiation inactivation/target size analysis (Venter, 1983b; Venter et al, 1983b; Lilly et al., 1983), characterization of hydrodynamic properties (Davis, 1984), and immunological approaches using conventional antibodies, monoclonal antibodies, and antiidiotypic antibodies (Venter et al, 1984; Fraser and Venter, 1980; Venter, 1983a; Venter and Fraser, 1983; Berzofsky, 1984; Berzofsky et al., 1980, 1982; Tzartos and Linstrom, 1980; Gullick et al., 1982; Yavin et al., 1981; Beisiegel et al., 1981; Greene et al., 1980; Schreiber et al., 1980;Wasserman et al., 1982). This chapter will detail the monoclonal antibody approach that we have found to be successful in isolating and characterizing the structure of membrane transport proteins and hormone and neurotransmitter receptors.