High impact information on FUS1

• Inactivation of the Cln-Cdc28p kinase complex by thermal inactivation of temperature-sensitive Cdc28p prevented repression of FUS1 signaling [1].
• G2/M-phase and pre-Start cells showed strong FUS1 mRNA induction, whereas in post-Start cells the signaling was reduced significantly [1].
• Here, we found that polarization of Fus1p, a raft-associated type I transmembrane protein involved in cell fusion, does not depend on endocytosis [2].
• We found that polarisome components and the cell fusion proteins Fus1 and Fus2 are important for the termination of projection growth [3].
• To understand how cell fusion is regulated, we identified mutants defective in cell fusion based upon their defect in mating to a fus1 fus2 strain (Chenevert, J., N. Valtz, and I. Herskowitz. 1994. Genetics 136:1287-1297) [4].

Biological context of FUS1

• From this screen we identified a gene, FUS1, whose pattern of expression revealed interesting regulatory strategies and whose product was required for efficient cell fusion during mating [5].
• Pheromone response elements are necessary and sufficient for basal and pheromone-induced transcription of the FUS1 gene of Saccharomyces cerevisiae [6].
• The FUS1 gene of Saccharomyces cerevisiae is transcribed in a and alpha cells, not in a/alpha diploids, and its transcription increases dramatically when haploid cells are exposed to the appropriate mating pheromone [6].
• The MOT2 gene encodes a putative zinc finger protein, the deletion of which resulted in temperature-sensitive growth, increased expression of FUS1 in the absence of pheromones, and suppression of a deletion of the alpha-factor receptor [7].
• These observations suggest that GPA1 (SGP1) and SGP2 are involved in mating factor-mediated signal transduction, which causes both cell cycle arrest in the late G1 phase and induction of genes necessary for mating such as FUS1 [8].

Anatomical context of FUS1

• Thus, Fus1 may be located at a position within the cell where it is poised to catalyze cell wall or plasma membrane fusion [5].
• In fus1 X fus1 matings, the cells of a mating pair adhered tightly and appeared to form zygotes [5].
• Genetic evidence suggests that the FUS2 gene product promotes cell fusion during zygote formation in Saccharomyces cerevisiae, functioning with the Fus1 plasma membrane protein at or before cell wall and plasma membrane fusion [9].
• Membrane fractionation and protease protection experiments indicate that FUS1 spans the plasma membrane, with its glycosylated amino terminus projecting into the periplasmic space [10].

Associations of FUS1 with chemical compounds

• Activation of FUS1 transcription in the mannose utilization/protein glycosylation mutants required some but not all proteins from three different signaling pathways: the pheromone response, invasive growth, and HOG pathways [11].
• This sequence suggests that FUS1 encodes a membrane-anchored glycoprotein with both N- and O-linked sugars [12].
• Induction of a pheromone-responsive FUS1-HIS3 reporter gene in far1 his3 cells permits cell growth in medium lacking histidine [13].
• We show that the FUS1 protein migrates on SDS/polyacrylamide gels with an apparent molecular mass of 80 kDa, although the mass is predicted to be 58 kDa from the gene coding capacity [10].
• We found that catecholamines (l-3,4-hydroxyphenylalanine [l-dopa], dopamine, adrenaline, and noradrenaline) elevate FUS1 and RLM1 transcription [14].

Regulatory relationships of FUS1

• We demonstrate here that strains harboring temperature-sensitive mutations in CDC36 or CDC39 activate expression of the pheromone-inducible gene FUS1 when shifted to nonpermissive temperature [15].
• The cell fusion defect associated with fus1Delta mutants is suppressed by a sho1Delta deletion allele, suggesting that Fus1p negatively regulates Sho1p signaling to ensure efficient cell fusion [16].
• Moreover, when exposed to hyperosmolarity, these Ste50p-SAM mutants activate genes in the mating (FUS1) and filamentous-growth (FLO11) pathways to higher levels than does the wild type [17].

Other interactions of FUS1

• Furthermore, the steady-state level of the FUS1 transcript, which normally increases in response to mating factors, was also elevated when the GPA1 function was impaired [18].
• In contrast, deletion of BEM1 resulted in decreased expression of FUS1, suggesting that Bem1p normally facilitates pheromone signaling [19].
• Analysis of Fus- zygotes indicated that Fus1p was required for the normal localization of the vesicles to the zone of cell fusion, and Spa2p facilitated their clustering [20].
• In addition, mating efficiency is much lower in fus1 fus2 x chs5 than in fus1 fus2 x wild type crosses [21].
• Furthermore, overexpression of GPA1 prevented cell-cycle arrest but not FUS1 induction mediated by overexpression of STE4 [22].

References