A testis-specifically expressed gene is embedded within a cluster of maternally expressed genes at 89B in Drosophila melanogaster.

Differential screening was used to isolate a genomic clone, lambda89Ba located at 89B that hybridised preferentially with female cDNA. On further investigation, a 3.1-kb subfragment, 89Ba(3.1), was shown to contain a gene with male germline-specific expression (Mst89B) flanked by two genes (Mat89Ba and Mat89Bb) expressed predominantly in the ovaries and embryo of Drosophila melanogaster. Mat89Bb is separated from Mst89B by at most 100 bp; Mst89B and Mat89Ba are convergently transcribed and their 3' untranslated regions (UTRs) overlap by a minimum of 85 bp. Database searches with either the 89Ba(3.1) genomic DNA sequence or conceptual translations of Mst89B or Mat89Bb cDNAs failed to reveal any significant similarities with database entries. Using in situ hybridisation to ovaries, Mat89Ba and Mat89Bb were shown to be expressed in nurse cells at stages nine and ten of oogenesis and exported to the oocyte. In addition, Mat89Bb transcripts were detected in the follicle cells surrounding the oocyte. Mst89B transcripts were present throughout spermatogenesis in germline-derived cells, consistent with northern analysis which showed that they were absent in the offspring of tudor flies that lack a germline. The absence of Mst89B transcripts at the tip of the testis suggested that the somatic cells in this region do not express Mst89B. Two 12-bp sequences were identified in the 5' UTR of Mst89B with a strong similarity to translational control elements (TCEs) originally identified in the CGP gene family. This suggests that TCEs may be present in a wider class of testis transcripts.