Mum2 is required for normal meiotic progression and
interacts with
Ime4 and Kar4, proteins with similarity to RNA
methyltransferases.
Stewart Morgan, JoAnne Engebrecht
Pharmacology, Suny @ Stony Brook, Stony Brook Univ., Stony Brook, NY
11794-8651, USA (morgan@pharm.sunysb.edu)
The MUM2 gene is essential for normal meiotic progression.
mum2 mutants display defects in premeiotic DNA replication,
double strand break formation, and arrest prior to the meiosis 1
division (Tsuboi et al, 1983; Engebrecht et al., 1998, Davis et al.,
2001). Previous studies have shown that premeiotic DNA replication
occurs subsequent to Ime2-dependent Sic1 degradation (Dirick et al.,
1998). Analysis of Sic1 levels in meiosis revealed that Sic1
degradation is delayed relative to wild type and occurs concomitant
with delayed premeiotic DNA replication in mum2
mutants. Consistent with this, FACS profiles ofmum2 sic1
mutants show that meiotic DNA replication occurs with similar kinetics
to the sic1 mutant; however, mum2 sic1 mutants still arrest
prior to meiosis I. These results indicate that Mum2 functions
upstream of Sic1 degradation and plays additional roles during
meiosis. Northern blot analysis reveals that the IME2
transcript is reduced and delayed relative to wild type while the
IME1 transcript is unaffected in mum2 mutants. This
suggests that Mum2 may mediate its function by impinging on the key
meiotic regulator, Ime2. Two-hybrid data (Uetz et al., 1998), meiotic
coimmunoprecipitations, and phenotypic analysis indicate that Mum2,
Kar4, and Ime4, all essential for normal meiotic progression, may
function in a complex to facilitate meiotic progression in S.
cerevisiae, perhaps through post-transcriptional modification of
meiotic transcripts.