Résumé
The Suppressor of forked (Su(f)) protein of
Drosophila melanogaster is a homologue of the 77K subunit of human cleavage stimulation factor required for cleavage of pre-mRNAs before addition of poly(A). We have previously shown that the Su(f) protein is not ubiquitously distributed: it accumulates in dividing cells at various stages of
Drosophila development. In this paper, we show that phenotypes of
su(
f) temperature-sensitive mutants result from a defect in cell proliferation. Analysis of the mitotic phenotype of
su(
f) temperature-sensitive alleles in larval brain and in imaginal discs reveals an increase in the number of metaphases with overcondensed chromosomes and asymmetric or reduced mitotic spindles. In contrast, neural differentiation in eye imaginal discs of the same mutant flies does not appear to be affected. These results indicate that
su(
f) is required during cell division for progression through metaphase. Taken together, these data suggest that a decrease in
su(
f) activity preferentially affects 3′-end formation of particular mRNAs, some of which are involved in mitosis, and are in agreement with a role of
su(
f) in the regulation of poly(A) site utilization.