A double RING-H2 domain in RNF32, a gene expressed during sperm formation

The RING domain is a cysteine-rich zinc-binding motif, which is found in a wide variety of proteins, among which are several proto-oncogenes and the gene implicated in autosomal recessive juvenile parkinsonism, Parkin. The domain mediates binding to other proteins, either via their RING domains or other motifs. In several proteins, RING domains are found in combination with other cysteine-rich binding motifs and some proteins contain two RING domains. Recent evidence suggests that RING finger proteins function in the ubiquitin pathway as E3 ligases. A variant of the RING domain is the RING-H2 domain, in which one of the cysteines is replaced by a histidine. We have cloned and characterized a novel gene, RNF32, located on chromosome 7q36. RNF32 is contained in 37 kb of genomic DNA and consists of 9 constitutive and 8 alternatively spliced exons, most of which are alternative first exons. A long and a short transcript of the gene are expressed; the short transcript containing exons 1-4 only. This gene encodes two RING-H2 domains separated by an IQ domain of unknown function. This is the first reported gene with a double RING-H2 domain. In humans, RNF32 overlaps with a processed retroposon located on the opposite strand, C7orf13. RNF32 is specifically expressed in testis and ovary, whereas C7orf13 is testis-specific, suggesting that its expression may be regulated by elements in the RNF32 promoter region. RNF32 is expressed during spermatogenesis, most likely in spermatocytes and/or in spermatids, suggesting a possible role in sperm formation.