The modifier of position-effect variegationSuvar(3)7 ofDrosophila: there are two alternative transcripts and seven scattered zinc fingers, each preceded by a tryptophan box

An increase in the number of copies of the Drosophila locus Suvar(3)7 enhances position-effect variegation, i.e. the inactivation in some cells of genes brought close to heterochromatin by a chromosomal rearrangement. The locus produces two transcripts of 5047 and 4203 nt that differ solely by the length of their 3' untranslated region. That these transcripts encode the modifier of variegation Suvar(3)7 is demonstrated by genetic transformation with the corresponding cDNAs. The deduced protein is 1169 amino acids long and contains seven widely spaced zinc fingers. These fingers are each preceded at 11-16 amino acids before the N-terminal cysteine by a tryptophan-containing motif. The transcripts are maternally transmitted, but are also found throughout development. The ubiquitous distribution of transcripts in embryos and the different sequence motifs support our speculation that the locus encodes a chromosomal protein implicated in heterochromatin-mediated DNA silencing.