Flocculation inSaccharomyces cerevisiae is regulated by RNA/DNA helicase Sen1p

Abstract

a b s t r a c tThe Nrd1-Nab3-Sen1 (NNS) complex terminates transcription of non-coding RNA genes and mediates degradation of the produced transcript by the nuclear exosome. The NNS complex also represses some stress response genes, by stimulating premature termination. A well-characterized stress response in yeast is flocculation, where cells aggregate to form flocs under expression of lectin-encoding genes designated as FLOs. In this study, we demonstrated the role of the NNS complex and Rrp6p in the expression of flocculation genes: FLO1, FLO5, FLO9, and FLO10. Furthermore, a deletion mutant of the RNA processing machinery (RNT1), and SEN1 mutants that are unable to interact with Rnt1p, exhibit a flocculation phenotype. In summary, we have identified a cooperative role of Rnt1p, Rrp6p and the NNS complex in the repression of FLO genes.

Flocculation of Saccharomyces cerevisiae is dependent on activation of Slt2 and Rlm1 regulated by the cell wall integrity pathway

“…Previous work by our group has shown constitutive expression of FLO genes in the Sen1 , Nab3 mutants and rnt1Δ cells leading to calcium‐dependent flocculation/aggregation of cells (Singh et al , ). Later, another study showed expression of the FLO1 gene in the Sen1 mutant (Chen et al , ).…”

“…We focused our studies to find whether or not flocculation phenotype is connected with cellular morphology, cell wall composition and growth in response to cell wall damaging agents. Previously, we established that the de‐repression of FLO genes in Sen1 , Nab3 and Rnt1 mutants lead to flocculation phenotype (Singh et al , ). One recent report (Chen et al , ) has also shown up‐regulation of FLO1 mRNA in Sen1 mutant strain suggesting the contribution of Sen1 in the regulation of flocculation phenotype.…”

“…After settling, the optical density of the yeast suspensions in the presence or absence of Ca 2+ was measured. The extent of flocculation is determined by the following equation: F = (1− B / A ) × 100% as described previously (Singh et al , ) where A is the OD 600 without Ca 2+ , B is the OD 600 with Ca 2+ and F is the flocculation ability. The percentage of flocculation is represented as the mean of three independent biological replicates.…”

“…S4C). Previously, we reported the flocculation phenotype of the mutants of Sen1, Nrd1, Nab3 and rnt1Δ (Singh et al, 2015), but the connection with the CWI pathway was not established. These results suggest that the activation of the CWI pathway (phosphorylation of Slt2) is functionally linked with flocculation of yeast cells.…”

“…sen1‐K128E and sen1‐R302W , reduce the binding affinity of Sen1p with Rnt1p and Rpb1p respectively (Finkel et al , ). We had previously reported the flocculation phenotype in sen1‐1 , sen1 ΔN and sen1‐K128E mutant strains (Singh et al , ). Subsequently, another group also reported an increase in expression of FLO1 in sen1‐E1597K mutant (Chen et al , ).…”