INTERALLELIC COMPLEMENTATION AT THE SUPPRESSOR OF FORKED LOCUS OF DROSOPHILA REVEALS COMPLEMENTATION BETWEEN SUPPRESSOR OF FORKED PROTEINS MUTATED IN DIFFERENT REGIONS

The Su(f) protein of Drosophilia melanogaster shares extensive homolog ies with proteins from yeast (RNA14) and mall (77 kD subunit of cleava ge stimulation factor) that are required for 3' end processing of mRNA . These homologies suggest that su(f) is involved in mRNA 3' end forma tion and that some aspects of this process are conserved throughout eu karyotes. We have investigated the genetic and molecular complexity of the su(f) locus. The su(f) gene is transcribed to produce three RNAs and could encode two proteins. Using constructs that contain different parts of the locus, we show that only the larger predicted gene produ ct of 84 kD is required for the wild-type function of su(f). Some leth al alleles of su(f) complement to produce viable combinations. The str uctures of complementing and noncomplementing su(f) alleles indicate t hat 84-kD Su(f) proteins mutated in different domains can act in combi nation for partial su(f) function. Our results suggest protein-protein interaction between or within wild-type Su(f) molecules.