Requirement of Fission Yeast Cid14 in Polyadenylation of rRNAs

Polyadenylation in eukaryotes is conventionally associated with increased nuclear export, translation, and stability of mRNAs. In contrast, recent studies suggest that the Trf4 and Trf5 proteins, members of a widespread family of noncanonical poly(A) polymerases, share an essential function in Saccharomyces cerevisiae that involves polyadenylation of nuclear RNAs as part of a pathway of exosome-mediated RNA turnover. Substrates for this pathway include aberrantly modified tRNAs and precursors of snoRNAs and rRNAs. Here we show that Cid14 is a Trf4/5 functional homolog in the distantly related fission yeast Schizosaccharomyces pombe. Unlike trf4 trf5 double mutants, cells lacking Cid14 are viable, though they suffer an increased frequency of chromosome missegregation. The Cid14 protein is constitutively nucleolar and is required for normal nucleolar structure. A minor population of polyadenylated rRNAs was identified. These RNAs accumulated in an exosome mutant, and their presence was largely dependent on Cid14, in line with a role for Cid14 in rRNA degradation. Surprisingly, both fully processed 25S rRNA and rRNA processing intermediates appear to be channeled into this pathway. Our data suggest that additional substrates may include the mRNAs of genes involved in meiotic regulation. Polyadenylation-assisted nuclear RNA turnover is therefore likely to be a common eukaryotic mechanism affecting diverse biological processes

Inactivation of the Pre-mRNA Cleavage and Polyadenylation Factor Pfs2 in Fission Yeast Causes Lethal Cell Cycle Defects

Faithful chromosome segregation is fundamentally important for the maintenance of genome integrity and ploidy. By isolating conditional mutants defective in chromosome segregation in the fission yeast Schizosaccharomyces pombe, we identified a role for the essential gene pfs2 in chromosome dynamics. In the absence of functional Pfs2, chromosomal attachment to the mitotic spindle was defective, with consequent chromosome missegregation. Under these circumstances, multiple intracellular foci of spindle checkpoint proteins Bub1 and Mad2 were seen, and deletion of bub1 exacerbated the mitotic defects and the loss of cell viability that resulted from the loss of pfs2 function. Progression from G(1) into S phase following release from nitrogen starvation also required pfs2(+) function. The product of the orthologous Saccharomyces cerevisiae gene PFS2 is a component of a multiprotein complex required for 3′-end cleavage and polyadenylation of pre-mRNAs and, in keeping with the conservation of this essential function, an S. pombe pfs2 mutant was defective in mRNA 3′-end processing. Mutations in pfs2 were suppressed by overexpression of the putative mRNA 3′-end cleavage factor Cft1. These data suggest unexpected links between mRNA 3′-end processing and chromosome replication and segregation

Mammalian Fauna from the Neogene Sediments of Myanmar

The terrestrial Neogene sediments are widely exposed along the Ayeyarwady and Chindwin River in central Myanmar and they are divided into three major units: the Freshwater Pegu Beds (Oligocene? to middle Miocene), the Irrawaddy Formation (latest middle Miocene to the early Pleistocene) and the River Terrace deposits (middle to late Pleistocene). A variety of mammalian fossils has been recovered from these sediments and consists of 6 orders, 21 families and 49 genera: Primate (4 genera); Carnivora (4 genera); Artiodactyla (27 genera); Perissodactyla (6 genera) and Proboscidea (8 genera). Myanmar fauna is more similar to the South Asian fauna (Siwalik) than to the East Asian fauna in the Miocene. Faunal interchange between Myanmar and East Asia seems to have started in the late Miocene to the latest Miocene. Faunal interchange among South Asia, East Asia and Myanmar seems to have increased in the early to middle Pleistocene because northern fauna moved southward due to the cooling event in the northern hemispher

Two type V myosins with non-overlapping functions in the fission yeast Schizosaccharomyces pombe: Myo52 is concerned with growth polarity and cytokinesis, Myo51 is a component of the cytokinetic actin ring

The fission yeast genome project has identified five myosin genes: one type I myosin, myo1(+), two type II myosins, myo2(+) and myp2(+), and two type V myosins, myo51(+) and myo52(+). Cells deleted for myo51(+) show normal morphology and growth rates whereas deletion of myo52(+) results in a partial loss of cell polarity, slow growth and cytokinetic defects. Combining both deletions in a single strain is phenotypically non-additive, myo52(delta) being epistatic to myo51(delta). Overproduction of Myo51 gives rise to elongated cells which fail to form functional septa whereas overproduction of Myo52 results in branched cells with aberrant septa that fail to cleave. Myo52 localises to the poles of growing cells but during cell division it relocalises to the cell equator as a bar that is bisected by the cytokinetic septum. Myo51 shows no obvious localisation during interphase but at cytokinesis it is associated with the contractile cytokinetic actin ring (CAR). Both myosins are dependent upon an intact actin cytoskeleton for localisation. Myo52 partially colocalises with the (alpha)-glucan synthase Mok1 at the cell tips and to a lesser extent at the septum. Mok1 is delocalised and upregulated in myo52(delta) and myo52(delta) cell walls are resistant to digestion by the cell wall degrading enzyme zymolyase. Thus myo52(+) appears to be involved in the local delivery or positioning of vesicles containing cell wall precursors at the cell tips and has a role in the maturation or cleavage of the septum. Myo51 has a non-essential role in cytokinesis as a component of the cytokinetic actin ring