Photoreceptor mutant of Drosophila : is protein involved in intermediate steps of phototransduction?

In norpA mutants of Drosophila melanogaster the phototransduction process is either partially or completely blocked. By using a temperature-sensitive allele, we have found that the norpA mutation has little or no effect on either the rhodopsin-metarhodopsin transition or the machinery of quantum bump production. Thus, the norpA lesion appears to be localized in the intermediate process of phototransduction. Because a temperature-sensitive allele of norpA has been isolated, the norpA gene probably encodes a protein involved in the process.