A Drosophila gene containing the opa repetitive element is exclusively expressed in adult male abdomens.

A complementary DNA has been isolated from an adult Drosophila library that encodes a predicted protein of 69 amino acids (Mw = 8104) and an opa repetitive element. The gene was isolated using a genomic fragment during a walk upstream of a previously cloned gene, AP3 (1). This gene has been given the name Dromsopa (EMBL accession no. X56491) and has no other identity with genes currently in the databases, once the opa repeat is excluded. The 0.6 kb mRNA for this gene is only found in adult male abdomens and at no other time of Drosophila development or in any other adult body sections. Opa repeats are defined by the sequence CAXn where X is usually a G, A or C and encodes either glutamine (Gin: CAG and CAA) or histidine (His: CAC) and n = approximately 28 (2). The Dromsopa gene contains 26 CAX sequences. Homogeneous stretches of amino acids, particularly glutamines, are associated with homeobox genes in Drosophila. Although the opa gene is a short repetitive element, it occurs in a number of gene products and is, therefore, apparently translated. These genes include, but are not limited to, the genes listed in Table 1. It appears, from previously identified opa containing genes that these genes are involved in cell-type-specific functions in vertebrates, are not randomly distributed in mRNAs, and can be found in mRNAs transcribed in an adult tissue-specific manner (3). These opa repeats have been found in a wide range of genes that are under developmental or tissue specific control from yeast to humans (Table 1).