Evidence that two mutations, w^DZL and z¹, affecting synapsis-dependent genetic behavior of white are transcriptional regulatory mutations

Both the white mutant allele, w^DZL, 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, w^DZL 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, w^DZL and z¹ are known to cause synapsis-dependent repression of w¹ 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.