Résumé
The Suppressor of forked protein is the Drosophila
homolog of the 77K subunit of human cleavage stimulation
factor, a complex required for the first step of the mRNA
3′-end-processing reaction. We have shown previously
that wild-type su(f) function is required for
the accumulation of a truncated su(f) transcript
polyadenylated in intron 4 of the gene. This led us to
propose a model in which the Su(f) protein would negatively
regulate its own accumulation by stimulating 3′-end
formation of this truncated su(f) RNA. In this
article, we demonstrate this model and show that su(f)
autoregulation is tissue specific. The Su(f) protein accumulates
at a high level in dividing tissues, but not in nondividing
tissues. We show that this distribution of the Su(f) protein
results from stimulation by Su(f) of the tissue-specific
utilization of the su(f) intronic poly(A) site,
leading to the accumulation of the truncated su(f)
transcript in nondividing tissues. Utilization of this
intronic poly(A) site is affected in a su(f) mutant
and restored in the mutant with a transgene encoding wild-type
Su(f) protein. These data provide an in vivo example of
cell-type-specific regulation of a protein level by poly(A)
site choice, and confirm the role of Su(f) in regulation
of poly(A) site utilization.