A DELETION IN THE 2ND CYTOPLASMIC LOOP OF GLUR3 PRODUCES A DOMINANT-NEGATIVE MUTANT OF ALPHA-AMINO-3-HYDROXY-5-METHYL-4-ISOXAZOLE PROPIONIC-ACID RECEPTOR

We have characterized a GluR3 mutant (sGluR3) which has a 33-amino aci d deletion in its second cytoplasmic loop (deficit from Tyr-715 to Gly -747 of GluR3-flop). Xenopus oocytes injected with cRNA transcribed fr om cDNA for this mutant did not respond to kainate and glutamate (each 100 mu M) at a holding potential of -70 mV. In oocytes coinjected wit h cRNAs for this mutant and for normal alpha-amino-3-hydroxy-5-methyl- 4-isoxazole propionic acid (AMPA) receptor subunits, the current respo nse to both kainate and glutamate was much weaker than that observed i n oocytes injected with cRNA for the normal subunits alone. This inhib itory action was not accompanied by a significant change of ED(50) val ue and shape of the I-V curve and was AMPA receptor-specific, A compar able deletion in GluR1 produced a mutant with properties similar to th ose of sGluR3, while a 33-amino acid deletion elsewhere in the second cytoplasmic loop of GluR3 (Met-674 to Phe-706) gave a mutant with a we aker effect. These results suggest that sGluR3 acts as a dominant nega tive mutant on the functional expression of normal AMPA receptors in o ocytes by assembling with the normal subunits to produce an essentiall y nonfunctional receptor complex.