Evidence that two mutations, wDZL and z1, affecting synapsis-dependent genetic behavior of white are transcriptional regulatory mutations.

Both the white mutant allele, wDZL, and the zeste mutant allele, z1, reduce white transcript levels in adult head tissues, but have no effect on these levels in other tested adult tissues. wDZL results from insertion of a complex transposon approximately 5.0 kb 5' to white. Juxtaposition of this transposon to white produces a novel transcription unit beginning in the transposon and producing a mature transcript containing both white and transposon sequences. Head-specific expression of this novel transcription unit correlates with the observed repression of wild-type white transcript levels. wDZL and z1 are known to cause synapsis-dependent repression of w+ expression in trans as assessed by eye pigment deposition. Collectively, these results suggest an unexpected and informative correspondence between cis and synapsis-dependent trans regulatory effects. We discuss the implied mechanistic relationship between regulation of transcription and transvection effects in Drosophila.