Blastoderm-specific and read-through transcription of the sry alpha gene transformed into the Drosophila genome.

The serendipity (sry) locus contains three tightly clustered genes: beta, alpha, and delta. The alpha gene lies between beta and delta and is expressed predominantly at the blastoderm stage of embryogenesis. Additional features of this locus include read-through transcription and the fact that the predicted beta and delta polypeptides show remarkable homology to the Xenopus RNA polymerase III transcription factor TFIIIA. To identify cis-acting elements controlling the expression of the alpha and beta transcripts, we created transformed lines containing modified versions of these genes. In lines containing derivatives of both the alpha and beta genes, the expected modified mRNAs are transcribed. An alpha gene variant containing only 798 bp of upstream DNA is also transcribed, and at the proper time; thus blastoderm-specific alpha gene transcription is independent of expression of the adjacent upstream beta gene. Analysis of transformed lines confirmed the beta-alpha read-through transcription, which was eliminated by the insertion of a different polyadenylation site within the coding region of the beta gene. We conclude that the transcription of the beta and alpha genes is independently regulated.