INSERTIONS OF HYBRID-P-ELEMENTS IN THE YELLOW GENE OF DROSOPHILA CAUSE A LARGE VARIETY OF MUTANT PHENOTYPES

A series of yellow mutations associated with a great variety of tissue -specific phenotypes were obtained from several highly unstable Drosop hila melanogaster strains carrying the gypsy-induced y(2) allele. Thes e mutations are caused by insertion of additional DNA sequences of var iable size 69 bp upstream of the yellow transcription start site. Thes e sequences are flanked by identical copies of a deleted 1.2-kb P elem ent arranged in the same or inverted orientation. The central part of the inserted element consists of genomic sequences originating from di fferent regions of the X chromosome. The mutant phenotype caused by th ese chimeric elements depends on the nature of the sequences present e ither in the P element or in the central part of the insertion, sugges ting that these sequences are able to affect expression of the yellow gene. In addition, sequences present in the central region of the inse rtions strongly modify the effects of the gypsy-bound suppressor of Ha iry-wing [su(Hw)] and modifier of mdg4 [mod(mdg4)] proteins on yellow transcription. Analyses of these mutations give new insights into the mechanisms by which su(Hw) and mod(mdg4) affect enhancer function.