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Running title: Mouse cones require an arrestin Nikonov et al. Generation and confirmation of Arr4−/ − mice The gene target strategy for creation of Arr4−/ − mice is described in the text of the paper (text Fig. 1). The targeting vector was confirmed first by restriction analysis after each modification step, and then verified by dideoxy sequence analysis using primers designed to read from the LacZ/Neo cassette into the 3 ’ end of the LA (LZ1) and the 5 ’ end of the SA (N1), or from primers that anneal to the vector sequence, P6 and T7, and read into the 5 ’ and 3’ ends of the BAC subclone. Ten micrograms of the targeting vector were linearized by NotI and then transfected by electroporation of 129/Svev embryonic stem (ES) cells (InGenious Targeting Laboratory Inc.). After selection in G418, 300 surviving clones were expanded for PCR analysis to identify recombinant ES clones. Oligonucleotide probes for PCR screening were as follows