Program of the 2001 International Worm Meeting - Sternberg Lab ...

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lengthened interphase and M phase, and
inappropriate DNA replication. In addition, we
find that phosphorylation of NCC-1 (C. elegans
cdc2, Boxem et al., 1999) is reduced in ax224
mutants (Thanks to Andy Golden for the NCC-1
antibody). Finally, the cdk-7(RNAi);
cdk-7(ax224) "double mutant", which
presumably lacks most cdk-7 activity, arrests in
the one-cell stage with a phenotype similar to
that observed in ncc-1(RNAi) embryos. Taken
together, our data demonstrates that cdk-7 has
independent roles in transcriptional activation
and cell cycle control, and suggests that cdk-7
may be the sole essential CAK in C. elegans.
42. A novel protein required for
degradation of CCCH finger proteins
in somatic lineages.
Kim Reese 1 , Geraldine Seydoux 2
1 Dept. of Molecular Biology and Genetics.
Johns Hopkins U. School of Medicine.
Baltimore MD 21205.
2 Dept. of Molecular Biology and Genetics.
Johns Hopkins U. School of Medicine.
Baltimore MD 21205
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The first cleavages of the embryo are
asymmetric and give rise to 5 somatic lineages
and the embryonic germ lineage. Several
maternal proteins are asymmetrically segregated
during these cleavages: in particular three
proteins, PIE-1, POS-1 and MEX-1, segregate
preferentially with the germ lineage and are
excluded from somatic lineages. These proteins
have in common a pair of CCCH zinc fingers
(ZF1 and ZF2). We have found that, when fused
to GFP, ZF1s from PIE-1, MEX-1 and POS-1
cause GFP to be degraded specifically in
somatic blastomeres. Consistent with a role in
protein degradation, mutations in PIE-1 ZF1
cause abnormal stabilization of PIE-1 in somatic
blastomeres. These observations suggest that the
ZF1 in PIE-1, MEX-1 and POS-1 targets these
proteins for degradation specifically in somatic
blastomeres.
To identify factors that function in this process,
we performed a yeast-two hybrid screen for
proteins that interact with PIE-1 ZF1 and
identified a novel protein, F59B2.6 (thanks to
Zheng Zhou and Bob Horvitz for their excellent
library). F59B2.6 does not appear to have any
recognizable motifs. GST pull down
experiments have confirmed that F59B2.6
interacts directly and specifically with ZF1 and
does not interact with ZF2. RNA-mediated
interference of F59B2.6 causes abnormal
accumulation of PIE-1,MEX-1 and POS-1 in
somatic blastomeres, and results in embryonic
lethality. F59B2.6(RNAi) embryos show no
defects in PAR-2, PAR-6 and GLP-1
localization, indicating that this gene is not
generally required for embryonic polarity. These
observations suggest that F59B2.6 recognizes
ZF1-containing proteins and targets them for
degradation in somatic blastomeres. Although
CCCH fingers in other proteins (e.g.
mammalian TIS11) have been implicated in