Functions as signal transducer for the rod photoreceptor RHO. Required for normal RHO-mediated light perception by the retina (By similarity). Guanine nucleotide-binding proteins (G proteins) function as transducers downstream of G protein-coupled receptors (GPCRs), such as the photoreceptor RHO. The alpha chain contains the guanine nucleotide binding site and alternates between an active, GTP-bound state and an inactive, GDP-bound state. Activated RHO promotes GDP release and GTP binding. Signaling is mediated via downstream effector proteins, such as cGMP-phosphodiesterase (By similarity). Heterotrimeric G proteins are composed of 3 subunits alpha, beta and gamma. The alpha chain contains the guanine nucleotide binding site. Interacts with RHO. Interacts with RGS9 and PDE6G (By similarity). Interacts (when myristoylated) with UNC119; interaction is required for localization in sensory neurons (By similarity). Localizes mainly in the outer segment in the dark-adapted state, whereas is translocated to the inner part of the photoreceptors in the light-adapted state. During dark-adapted conditions, in the presence of UNC119 mislocalizes from the outer segment to the inner part of rod photoreceptors which leads to decreased photoreceptor damage caused by light. Rod. Belongs to the G-alpha family. G(i/o/t/z) subfamily.