Required for the differentiation of photoreceptor cells. Plays a role in the organization of outer segment of rod and cone photoreceptors (By similarity). Interacts with RP1; has a synergistic effect with RP1 in photoreceptor differentiation. Localized to the axoneme of outer segments and connecting cilia in rod photoreceptors. Retinal-specific; expressed in photoreceptor. The C-terminal part contains a large repetitive region which contains an unusually high percentage of glutamine, glycine and above all glutamic acid residues. The exact length of RP1L1 is variable between individuals due to the presence of several length polymorphisms. The sequence shown here is that of allele RP1L1-1 and includes 3 repeats (from aa 1292-1342) with a length of 16 amino acids. The number of repeats is highly polymorphic and varies among different alleles, ranging from 3 to 8. The disease is caused by variants affecting the gene represented in this entry. The disease may be caused by variants affecting the gene represented in this entry. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.