Rod photoreceptors generate reproducible responses to single absorbed photons in a graded and systematic manner that is dependent upon the number of phosphorylation sites in rhodopsin’s C terminus. Wildtype mouse rhodopsin has six phosphorylation sites.
In these 2P compound mutant mice, the native mouse Rho (rhodopsin) gene has been knocked out and a transgene replacing two of the functional phosphorylation sites (S334 and S338) has been introduced. The remaining phosphorylation sites in the Rho transgene (T336, T340, T342 and S343) are inactivated via serine or threonine to alanine mutations. An A337V mutation was introduced to confer a linear epitope for mAb3A6, that allows specific recognition of transgenic versus endogenous opsin.
Compound mutant mice in which only the S338 phosphorylation site has been replaced (1P; see Stock No. 027644) or only the S334 and S338 phosphorylation sites have been replaced (2P) generate single-photon responses with greatly prolonged, exponentially distributed durations. Responses from rods expressing mutant rhodopsins bearing more than two phosphorylation sites (e.g. the 5P mutant mice whose transgene incorporates the S334, T336, S338, T340, T342 sites; see Stock No. 027646) decline along smooth, reproducible time courses. The rate of recovery increases with increasing numbers of phosphorylation sites.
