TRP and TRPL are two light-sensitive cation channel subunits required for t
he Drosophila photoresponse; however, our understanding of the identities,
subunit composition, and function of the light-responsive channels is incom
plete. To explain the residual photoresponse that remains in the trp mutant
, a third TRP-related subunit has previously been proposed to function with
TRPL. Here, we identify such a subunit, TRP gamma. We show that TRP gamma
is highly enriched in photoreceptor cells and preferentially heteromultimer
izes with TRPL in vitro and in vivo. The N-terminal domain of TRP gamma dom
inantly suppressed the TRPL-dependent photoresponse, indicating that TRP ga
mma-TRPL heteromultimers contribute to the photoresponse. While TRPL and TR
P gamma homomultimers are constitutively active, we demonstrate that TRPL-T
RP gamma heteromultimers form a regulated phospholipase C- (PLC-) stimulate
d channel.