Extended Gene Family Research Articles

A Family of Putative Potassium Channel Genes in Drosophila

Mutant flies in which the gene coding for the Shaker potassium channel is deleted still have potassium currents similar to those coded by the Shaker gene. This suggests the presence of a family of Shaker-like genes in Drosophila. By using a Shaker complementary DNA probe and low-stringency hybridization, three additional family members have now been isolated, Shab, Shaw, and Shal. The Shaker family genes are not clustered in the genome. The deduced proteins of Shab, Shaw, and Shal have high homology to the Shaker protein; the sequence identity of the integral membrane portions is greater than 50 percent. These genes are organized similarly to Shaker in that only a single homology domain containing six presumed membrane-spanning segments common to all voltage-gated ion channels is coded by each messenger RNA. Thus, potassium channel diversity could result from an extended gene family, as well as from alternate splicing of the Shaker primary transcript.

Affinity labelling of neuronal acetylcholine receptors localizes acetylcholine-binding sites to their β-subunits

Neuronal nicotinic acetylcholine receptors (AChRs) from brains of chickens and rats consist of two types of subunits, α and β, of which a shares some antigenic determinants with α-subunits from AChRs of electric organ and muscle [(1986) Biochemistry 25, 2082-2093; (1986) J. Neurosci. G, 3061-3069; (1986) Proc. Natl. Acad. Sci. USA, in press]. Here we demonstrate that after reduction with dithiothreitol (DTT) the AChRs can be specifically labelled with the acetylcholine-binding site directed reagent 4-( N-maleimido)benzyltri [ 3H]methylammonium iodide. Labelling of the β-subunits of neuronal nicotinic AChRs indicates that the acetylcholine-binding site, and amino acids which may be homologous to Cys 192–193 of the α-subunits of AChRs from electric organ and muscle, are located on the β-subunit of neuronal AChRs. These results suggest that although neuronal nicotinic AChRs have some structural homologies to AChRs from muscle and electric organs, the AChRs from these sources are quite distant relatives in an extended gene family.