We have characterized this gene, which we named cGAS-like receptor (cGLR) 2 (cGlr2 in FlyBase). The currently annotated methionine of the cGlr2-PD isoform is situated in the active site of the nucleotidyl transferase and would be incompatible with the fold of a cyclic dinucleotide synthase. There is another methionine in frame (in exon 1) in the cGlr2-RD@ transcript, with a better translation initiation consensus (gaaaaaATGaag), which produces a functional enzyme (starting by MKESRNLE...).
From FlyBase (LC): Thanks for the heads-up concerning this gene model annotation. We have looked at the current FlyBase gene model for cGlr2 and agree that the cGlr2-RD transcript needs to be reannotated with the upstream Met you have indicated.
This would result in what we term "multiphasic exons" -- the extended ORF of -RD overlaps the amino ends of the cGlr2-RB and cGlr2-RE, but in a different reading frame. This is an atypical situation (not unheard of, but rare).