Human and bovine rod photoreceptor cGMP-gated cation channel consists of two subunits: α (63 M)a) and β (240 kDa). The human β subunit was shown to consist partly of sequence encoded by the cDNA clone hRCNC2b. Here we present the complete sequence of the human β subunit and demonstrate that the previously reported human GAR1 gene encoding a glutamate-rich protein (hGARP) encodes its N-terminal portion. Using PCR, RNA blot and genomic DNA analysis, we provide evidence that the β subunit is produced from a complex locus on chromosome 16 which is also capable of generating independent transcripts corresponding to GAR1 and the C-terminal two-thirds of the β subunit. The results indicate that the β subunit of the cGMP-gated cation channel is produced from an unusual locus consisting of more than one transcription unit.